Alberts, Hugo W. 1926. A Method For Calculating Linkage Values Genetics, 11: 235-248.

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Altenburg, Edgar and Muller, Hermann J. 1920. The Genetic Basis of Truncate Wing,—an Inconstant and Modifiable Character in Drosophila Genetics, 5: 248.

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Altenburg, Edgar and Muller, Hermann J. 1920. The Genetic Basis of Truncate Wing,—an Inconstant and Modifiable Character in Drosophila Genetics, 5: 1-59.

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Anonymous. 1844. Vestiges of the Natural History of Creation. London: John Churchill.

This is a full-text PDF image facsimile version of the entire 390-page original first edition.

In 1859, many had already begun to think deeply about the meaning and origin of creation. Fifteen years before the Origin, Vestiges of the Natural History of Creation appeared, published anonymously. In one sense, the book is hopelessly dated, and amateurish to boot. In another, the book is incredibly modern - an effort, in the author's own words, "to connect the natural sciences into a history of creation."

At one point, the author (revealed in the 12th edition to be Robert Chambers) uses the example of Charles Babbage's calculating engine (the first computer) to show how apparently miraculous changes might occur as the result of subtle changes in an underlying governing system.

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Aristotle. 350 BC. On the Generation of Animals.

This is a full-text HTML version of the entire book.

Any collection of critical works in the history of biology must include works by Aristotle. Here, in On the Parts of Animals, Aristotle provides one of the world's first efforts to understand life in terms of its component parts.


Aristotle. 350 BC. On the Parts of Animals.

This is a full-text HTML version of the entire book.

Any collection of critical works in the history of biology must include works by Aristotle. Here, in On the Parts of Animals, Aristotle provides one of the world's first efforts to understand life in terms of its component parts.


Aristotle. 350 BC. The History of Animals.

This is a full-text HTML version of the entire book.

Any collection of critical works in the history of biology must include works by Aristotle. Here, in The History of Animals, Aristotle provides a discussion of the diversity of life, with considerable attention to reproduction and heredity.


Bateson, William, Saunders, E. R., and Punnett, R. C. 1904. Experimental Studies in the Physiology of Heredity. Reports to the Evolution Committee of the Royal Society, II, 1904, pp. 1-131

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William Bateson was the first English-speaking scientist to appreciate the potential significance of Mendel's work. He and his co-workers began immediately to confirm and extend Mendel's findings. This report to the evolution committee of the Royal Society represents one of the very first systematic investigations into Mendelism as a possible general explanation for the fundamental mechanisms of heredity.


Bateson, William, and Saunders, E. R. 1902. The facts of heredity in the light of Mendel's discovery. Reports to the Evolution Committee of the Royal Society, I, 1902, pp. 125-160

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William Bateson was the first English-speaking scientist to appreciate the potential significance of Mendel's work. He began working immediately to confirm and extend Mendel's findings. This report to the evolution committee of the Royal Society represents one of the very first systematic investigations into Mendelism as a possible general explanation for the fundamental mechanisms of heredity.


Bateson, William. 1894. Materials for the Study of Variation. London: Macmillan and Company.

This is a full-text PDF image facsimile version of the entire 598-page original first edition.

William Bateson was the first English-speaking scientist to recognize the significance of Mendel's work. Before the rediscovery of Mendel's work in 1900, Bateson had been active in studying morphology, with a special interest in discontinuous variation as it might apply to the origin of species.

In this book Bateson summarizes his observations on discontinuous variation. His concern for this kind of variation probably contributed greatly to the quickness with which he grasped the significance of Mendel's work.

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Bateson, William. 1899. Hybridisation and cross-breeding as a method of scientific investigation. Journal of the Royal Horticultural Society, 24:59-66.

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In this talk, given in 1899, before Mendel's work had been rediscovered, Bateson gives his vision of what kind of research will be necessary to shed light on the processes of inheritance and evolution:

What we first require is to know what happens when a variety is crossed with its nearest allies. If the result is to have a scientific value, it is almost absolutely necessary that the offspring of such crossing should then be examined statistically. It must be recorded how many of the offspring resembled each parent and how many shewed characters intermediate between those of the parents. If the parents differ in several characters, the offspring must be examined statistically, and marshalled, as it is called, in respect of each of those characters separately.

One would be hard pressed to provide a better anticipation of the experimental approach of Gregor Mendel. Small wonder that Bateson, upon encountering Mendel's work, quickly became convinced that the correct method for studying inheritance was finally at hand.


Bateson, William. 1900. Problems of heredity as a subject for horticultural investigation. Journal of the Royal Horticultural Society, 25:54-61.

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Mendel's work of 1865 was largely neglected, until 1900 when it was simultaneously rediscovered by Hugo de Vries, Carl Correns, and Erik von Tschermak. When Mendel's work came to the attention of William Bateson (who himself had already been advocating controlled crosses as an approach to studying heredity), he was convinced that Mendel's work was of major importance:

That we are in the presence of a new principle of the highest importance is, I think, manifest. To what further conclusions it may lead us cannot yet be foretold.

Bateson devoted the remainder of his scientific career to further elucidations of "Mendelism." This present paper captures the enthusiasm of Bateson's first encounter with the works of Mendel.


Bateson, William. 1902. Application for Support of an Experimental Investigation of Mendel's Principles of Heredity in Animals and Plants. In Bateson, B. 1928. William Bateson, F.R.S.: His Essays & Addresses, together with a Short Account of his Life. Cambridge: Cambridge University Press.

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Although not considered to be one of the "official" rediscovers of Mendel's work, William Bateson was the first English-speaking scientist to recognize the importance of Mendel's work and he immediately set out to bring Mendel's work to the attention of the scientific community. Bateson coined the word "genetics" to name the new field and made many important contributions to its development.

This present document is a copy of a letter that Bateson wrote in 1902, seeking financial support from the Trustees of the Carnegie Institution for continued investigations into Mendelian mechanisms of inheritance.

The letter was almost certainly the world's first grant application in the new field of genetics. It was declined.


Bateson, William. 1902. Mendel's Principles of Heredity: A Defence. London: Cambridge University Press.

This is a full-text PDF image facsimile version of the entire 212-page original first edition.

William Bateson was the first English-speaking scientist to recognize the significance of Mendel's work. In an 1899 paper, he had anticipated the sort of experimental design that Mendel used, and in 1900, shortly after Mendel's rediscovery, he published another paper in which he summarized Mendel's work in English, declaring it to be "a new principle of the highest importance."

In the present work, Bateson offers a book-length presentation of Mendel's approach to genetic research, including the first English translation of both Mendel's work on peas and his later work on Hieracium. The book is subtitled A Defence because the Mendelian approach to genetics was initially strongly resisted by the biometrician school, which based their thinking on Galton's ancestral law of heredity.

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Bateson, William. 1908. The Methods and Scope of Genetics. London: Cambridge University Press.

This is a newly typeset full-text version of the entire 49-page original first edition.

This short book is a copy of the Inaugeral Address, given by Bateson upon the creation of the Professorship of Biology at Cambridge. In his introduction, Bateson notes:

The Professorship of Biology was founded in 1908 for a period of five years partly by the generosity of an anonymous benefactor, and partly by the University of Cambridge. The object of the endowment was the promotion of inquiries into the physiology of Heredity and Variation, a study now spoken of as Genetics.

It is now recognized that the progress of such inquiries will chiefly be accomplished by the application of experimental methods, especially those which Mendel’s discovery has suggested. The purpose of this inaugural lecture is to describe the outlook over this field of research in a manner intelligible to students of other parts of knowledge.


Here then is a view of how one of the very first practitioners of genetics conceived of the "Methods and Scope of Genetics".


Beadle, G. W. 1935. Crossing Over Near the Spindle Attachment of the X Chromosomes in Attached-x Triploids of Drosophila Melanogaster Genetics, 20:179-191.

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Beadle, G. W. 1937. Development of Eye Colors in Drosophila: Fat Bodies and Malpighian Tubes in Relation to Diffusible Substances Genetics, 22: 587-611.

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Beadle, G. W. and Emerson, Sterling 1935. Further Studies of Crossing Over in Attached-x Chromosomes of Drosophila Melanogaster Genetics, 20: 192-206.

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Beadle, G. W. and Ephrussi, Boris 1936. The Differentiation of Eye Pigments in Drosophila As Studied by Transplantation Genetics, 21: 225-247.

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Beadle, G. W. and Ephrussi, Boris 1937. Development of Eye Colors in Drosophila: Diffusible Substances and Their Interrelations Genetics, 22: 76-86.

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Belling, John 1933. Crossing Over and Gene Rearrangement in Flowering Plants Genetics, 18: 388-413.

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Bridges, C. B. and Bridges, P. N. 1938. Salivary Analysis of Inversion-3r-payne in the "venation" Stock of Drosophila melanogaster Genetics, 23: 111-114.

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Bridges, Calvin B. 1914. Direct proof through non-disjunction that the sex-linked genes of Drosophila are borne on the X-chromosome. Science, NS vol. XL:107-109.

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Although Bridges' longer 1916 Genetics paper (vol 1, page 1) on the same topic is better known and treats the issue at much greater length, this short communication in Science contains the same argument and is equally persuasive.

By 1910, much evidence had been presented to demonstrate that sexual phenotype (i.e., maleness or femaleness) was determined by chromosomes. And, as early as 1902 Sutton noted that similarities in the behavior of genes and chromosomes suggested that Mendelian factors might be carried on chromosomes.

Here, Bridges shows that mis-assortment of the sex chromosomes is accompanied by atypical inheritance patterns for sex-linked traits and he argues that this proves that genes are carried on chromosomes. He concludes his paper: "there can be no doubt that the complete parallelism between the unique behavior of the chromosomes and the behavior of sex-linked genes and sex in this case means that the sex-linked genes are located in and borne by the X-chromosomes."


Bridges, Calvin B. 1916. Non-disjunction as proof of the chromosome theory of heredity (part 1). Genetics, B, 1:1-52.

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This paper was published as the first article in the first volume the new journal genetics. As the title states, the paper offered PROOF that genes are real, physical things that are carried on chromosomes.

This article was scanned from Alfred Sturtevant's personal copy of Genetics. Access to the journal was provided by Edward B. Lewis and Elliot M. Meyerowitz of the California Institute of Technology.


Bridges, Calvin B. 1916. Non-disjunction as proof of the chromosome theory of heredity (part 2). Genetics, B, 1:107-163.

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This paper was published as the first article in the first volume the new journal genetics. As the title states, the paper offered PROOF that genes are real, physical things that are carried on chromosomes.

This article was scanned from Alfred Sturtevant's personal copy of Genetics. Access to the journal was provided by Edward B. Lewis and Elliot M. Meyerowitz of the California Institute of Technology.


Bridges, Calvin B. 1917. Deficiency. Genetics, 2:445-465.

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Bridges, Calvin B. and Mohr, Otto L. 1919. The Inheritance of the Mutant Character "vortex" Genetics, 4: 283-306.

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Bridges, Calvin B., Skoog, Eleanor Nichols, and Li, Ju-chi. 1936. Genetical and cytological studies of a deficiency (notopleural) in the second chromosome of Drosophila melanogaster. Genetics, 21:788-795.

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Bridges, Calvin B., and Anderson, E. G. 1925. Crossing over in the X chromosomes of triploid females of Drosophila melanogaster.. Genetics, 10:418-441.

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Bridges, Calvin B., and Mohr, Otto L. 1919. The inheritance of the mutant character "vortex". Genetics, 4:283-306.

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Bridges, Calvin B., and Olbrycht, T. M. 1926. The Multiple Stock "xple" and its use. Genetics, 11:41-55.

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Bridges, Calvin. 1921. Triploid intersexes in Drosophila melanogaster. Science, 54:252-254.

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Work in the laboratory of T. H. Morgan was critical in establishing that genes are real, physical entities and that they are arranged in a linear order on chromosomes. Calvin Bridges was a key player in the Morgan group. In 1914, Bridges first demonstrated that a correlation existed between the incorrect assortment of X chromosomes and the incorrect assortment of some genes. In 1916, he expanded on that work to "prove" that sex-linked genes in Drosophila are carried on the X chromosome.

In this paper, Bridges shows that the correlation between mis-assortment of genes and chromosomes applies to the autosomes as well as to the sex chromosomes. In addition, he shows that sex determination in Drosophila appears to be driven by the ratio of X chromosomes to autosomes, not by the absolute number of X chromosomes.


Brink, R. A. and Cooper, D. C. 1935. A Proof That Crossing Over Involves an Exchange of Segments Between Homologous Chromosomes Genetics, 20: 22-35.

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Brooks, W. K. 1883. The Law of Heredity, Second Edition. Baltimore and New York: John Murphy & Co., Publishers.

This is a full-text PDF image facsimile version of the entire 336-page original first edition.

It is often thought that, besides Mendel, little work on heredity occurred during the 19th Century. This is far from true. Darwin's Origin of Species placed the study of inherited variation at the center of biological thought. As this work by Brooks attests, considerable effort was made to understand heredity, especially as it related to natural selection.

Although the details of Brooks' analysis are now outdated, the book provides general insights into late-nineteenth Century thinking on heredity. Since Brooks was one of T. H. Morgan's instructors when Morgan was a student at Johns Hopkins, the book also provides insights into the specific instruction on heredity that was presented to the man who became the first recipient of a Nobel Prize for work on genetics.

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Cannon, W. A. 1902. A cytological basis for the Mendelian laws. Bulletin of the Torrey Botanical Club, 29:657-661.

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Castle, W. E. 1938. The Relation of Albinism to Body Size in Mice Genetics, 23: 269-274.

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Castle, W. E. and Reed, S. C. 1936. Studies of Inheritance in Lop-eared Rabbits Genetics, 21: 297-309.

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Castle, W. E. 1911. Heredity in Relation to Evolution and Animal Breeding. New York: D. Appleton and Company

This is an image facsimile version of the entire 184-page original edition.




Castle, W. E. 1913. Simplification of Mendelian formulae. The American Naturalist, 47:170-182

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Soon after Mendel was rediscovered, the nature of the gene was being worked out. Along the way, many suggested changes to the symbology being used (e.g., B for dominant allele, b for recessive). Here Castle offers some suggestions for changing Mendelian symbols.


Castle, W. E. 1923. The relation of Mendelism to mutation and evolution. The American Naturalist, 57:559-561

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Here Castle offers a short note relating the behavior of simple Mendelian characters to the more complex, quantitative traits found in natural populations (and thus of interest to those studying evolution).


Castle, W. E. 1925. A Sex Difference in Linkage in Rats and Mice Genetics, 10: 580-582.

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Castle, W. E., Gates, W. H., Reed, S. C. and Law, L. W. 1936. Studies of a Size Cross in Mice, II Genetics, 21: 310-323.

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Castle, W. E., Gates, W. H., and Reed, S. C. 1936. Studies of a Size Cross in Mice Genetics, 21: 66-78.

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Castle, W. E., and Little, C. C. 1910. On a modified Mendelian ratio among yellow mice. Science, N.S., 32:868-870.

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Here, Castle and Little offer evidence consistent with the idea that the gene for yellow fur in mice, studied earlier by Cuénot, is probably lethal when carried homozygously.


Castle, W. E., and Wachter, W. L. 1924. Variations of Linkage in Rats and Mice Genetics, 9: 1-12.

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Castle, W.E. 1919. Is the arrangement of the genes in the chromosome linear? Proceedings of the National Academy of Sciences, 5:25-32.

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Charles W. Metz, Charles W. 1918. The Linkage of Eight Sex-linked Characters in drosophila Virilis Genetics, 3: 107-134.

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Cook, Robert. 1937. A chronology of genetics. Yearbook of Agriculture, pp. 1457-1477.

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Robert Cook, as editor of The Journal of Heredity, was especially well positioned to appreciate how the new science of genetics developed after the rediscovery of Mendel in 1900 and the establishment of the chromosome theory of inheritance by T. H. Morgan and his students.

In this essay, Cook traces the history of genetics to four main roots - mathematics, plant breeding, animal breeding, and cytology.


Correns, Carl 1900. G. Mendel's law concerning the behavior of progeny of varietal hybrids. First published in English as: Correns, C., 1950. G. Mendel's law concerning the behavior of progeny of varietal hybrids. Genetics, 35(5, pt 2): 33-41. Originally published as: Correns, C. 1900. G. Mendels Regel über das Verhalten der Nachkommenschaft der Rassenbastarde. Berichte der Deutschen Botanischen Gesellschaft, 18: 158-168.

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Correns, along with Hugo de Vries and Erik von Tschermak, is considered to be one of the three co-discovers of Mendel's work in 1900. Correns was the only one of the three to acknowledge Mendel in the title of his paper. Correns' paper begins:

The latest publication of Hugo de Vries: Sur la loi de disjonction des hybrides, which through the courtesy of the author reached me yesterday, prompts me to make the following statement: In my hybridization experiments with varieties of maize and peas, I have come to the same results as de Vries, who experimented with varieties of many different kinds of plants, among them two varieties of maize. When I discovered the regularity of the phenomena, and the explanation thereof - to which I shall return presently - the same thing happened to me which now seems to be happening to de Vries: I thought that I had found something new. But then I convinced myself that the Abbot Gregor Mendel in Brünn, had, during the sixties, not only obtained the same result through extensive experiments with peas, which lasted for many years, as did de Vries and I, but had also given exactly the same explanation, as far as that was possible in 1866.


Creighton, Harriet B., and McClintock, Barbara. 1931. A correlation of cytological and genetical crossing-over in Zea mays. PNAS, 17:492-497.

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When Alfred Sturtevant created the first genetic map, he hypothesized that genetic recombination resulted from the actual exchange of chromatid fragments. However, at the time there was no hard evidence that proved recombination is accomplished via such a mechanism. The same genetic results could be explained if only alleles are exchanged during recombination, leaving the bulk of the chromatid arm unaffected. Since the two hypotheses make equivalent predictions regarding the distribution of alleles, they cannot be distinguished using purely genetic methods.

Attempting to demonstrate that genetic recombination is accomplished via the physical exchange of chromatid arms poses a problem similar to that encountered by Thomas H. Morgan when he first hypothesized that genes might be carried on the X chromosome. Although Morgan’s genetic hypothesis of X-linkage provided an explanation for the inheritance of the white-eye allele in Drosophila, the notion that genes are actually carried on the X chromosome was not proven until Calvin Bridges provided cytological evidence to confirm the genetic observations. Bridges established a one-to-one correspondence between the abnormal distribution of eye-color alleles and the abnormal distribution of X chromosomes. That is, he established a relationship between genetic markers (the eye color alleles and their associated inheritance patterns) and cytological markers (the presence of abnormal sets of sex chromosomes).

In this paper, Creighton and McClintock present work in which they use a combination of cytological and genetic markers to show that cytological crossing-over occurs and that it is accompanied by genetical crossing-over.

At times, the authors’ discussion of their results can be difficult to follow. When this work was done, the authors could reasonably expect that any reader would be familiar with the underlying main question (is genetic and cytological recombination mediated by the same physical event?) and that readers would also be familiar with “chromosome mechanics” — that is, with interpreting experimental designs involving abnormal chromosomes. Because Creighton and McClintock could make such reasonable assumptions, they do not take much time to help readers understand the underlying logic or to appreciate the subtleties of the analysis. But, in just a few pages they do accomplish their goal of establishing the reality of cytological recombination and of showing that it is associated with genetic recombination. This paper is truly a classic paper.


Creighton, Harriet B., and McClintock, Barbara. 1931. A correlation of cytological and genetical crossing-over in Zea mays. PNAS, 17:492-497.

PDF image facsimile file: 6 pages - several figures

When Alfred Sturtevant created the first genetic map, he hypothesized that genetic recombination resulted from the actual exchange of chromatid fragments. However, at the time there was no hard evidence that proved recombination is accomplished via such a mechanism. The same genetic results could be explained if only alleles are exchanged during recombination, leaving the bulk of the chromatid arm unaffected. Since the two hypotheses make equivalent predictions regarding the distribution of alleles, they cannot be distinguished using purely genetic methods.

Attempting to demonstrate that genetic recombination is accomplished via the physical exchange of chromatid arms poses a problem similar to that encountered by Thomas H. Morgan when he first hypothesized that genes might be carried on the X chromosome. Although Morgan’s genetic hypothesis of X-linkage provided an explanation for the inheritance of the white-eye allele in Drosophila, the notion that genes are actually carried on the X chromosome was not proven until Calvin Bridges provided cytological evidence to confirm the genetic observations. Bridges established a one-to-one correspondence between the abnormal distribution of eye-color alleles and the abnormal distribution of X chromosomes. That is, he established a relationship between genetic markers (the eye color alleles and their associated inheritance patterns) and cytological markers (the presence of abnormal sets of sex chromosomes).

In this paper, Creighton and McClintock present work in which they use a combination of cytological and genetic markers to show that cytological crossing-over occurs and that it is accompanied by genetical crossing-over.

At times, the authors’ discussion of their results can be difficult to follow. When this work was done, the authors could reasonably expect that any reader would be familiar with the underlying main question (is genetic and cytological recombination mediated by the same physical event?) and that readers would also be familiar with “chromosome mechanics” — that is, with interpreting experimental designs involving abnormal chromosomes. Because Creighton and McClintock could make such reasonable assumptions, they do not take much time to help readers understand the underlying logic or to appreciate the subtleties of the analysis. But, in just a few pages they do accomplish their goal of establishing the reality of cytological recombination and of showing that it is associated with genetic recombination. This paper is truly a classic paper.

In a paper immediately preceding this one, McClintock provided the basic genetic and cytological information necessary to understand the experimental logic of this paper. The background paper is The order of the genes C, Sh, and Wx in Zea mays with reference to a cytologically known point in the chromosome.


Crew, F. A. E. 1969. Recollections of the early days of the genetical society. In John Jinks, The Genetical Society - The First Fifty Years, Edinburgh: Oliver and Boyd, pp.9-15.

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Darbishire, A. D. 1905. On the supposed antagonism of Mendelian to biometric theories of heredity. Manchester Memoirs, 49:1-19.

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Darwin, C. 1845. The Voyage of the Beagle, Second Edition. London: John Murray.

This is a full-text HTML version of the entire book.

For five years, from 1831-1836, Charles Darwin served as the official naturalist aboard the HMS Beagle as it visited exotic locations around the world. During this voyage, Darwin first came to wonder about the mechanisms driving the origin of species. This book chronicles the voyage and documents his early thinking.


Darwin, C. 1859. On the Origin of Species. London: John Murray, Albemarle Street.

This is a full-text PDF image facsimile version of the entire 502-page original first edition.

This is the book that changed the world and defined modern biology. By making mechanisms of heritable variation central to the biggest issue in all of biology, Darwin initiated the genetics revolution.


Darwin, C. 1883. The Variation of Animals and Plants Under Domestication, Second Edition, Revised (two volumes). New York: D. Appleton & Co.

This is a full-text PDF image facsimile version of the entire 473-page volume I and the entire 495-page volume II of the original work.

Although Darwin's theories regarding the origin of species through natural selection required that some mechanism of heredity exist, no such mechanism was known when the Origin was written. After the Origin appeared, Darwin turned his attention to the mechanism(s) of heredity, resulting in his subsequent two-volume The Variation of Animals and Plants Under Domestication.

In volume I, Darwin summarized what was known about inheritance in a variety of domesticated species and concluded with a chapter, Inheritance, that begins his general summary of the mechanisms of inheritance. He continued this summary in volume II, which also offers Darwin's own theory of inheritance in Chapter XXVII, Provisional Hypothesis of Pangenesis.

The notion of pangenesis dominated late nineteenth-century thinking about inheritance. Although ultimately seen to be simply wrong, it was very influential and a familiarity with its tenets is essential for anyone wishing to understand the intellectual climate at the time Mendel was rediscovered in 1900.

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Davenport, C. B. 1930. Sex linkage in man Genetics, 15: 401-444.

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Davenport, Charles B. 1917. Inheritance of Stature Genetics, 2: 313-389.

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David H. Thompson 1931. The side-chain theory of the structure of the Gene Genetics, 16: 267-290.

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Demerec, M. 1923. Inheritance of White Seedlings in Maize Genetics, 8: 561-593.

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Demerec, M. 1937. Frequency of Spontaneous Mutations in Certain Stocks of Drosophila melanogaster Genetics, 22: 469-478.

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Demerec, Milislav 1933. What is a Gene? Journal of Heredity, 24:368-378.

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Once the foundations of transmission genetics had been worked out, researchers began to consider what the chemical nature of the gene might be. Here Miroslav Demerec offers one of the first such efforts. He concludes that the gene is a minute organic particle, capable of reproduction, located in a chromosome and responsible for the transmission of a hereditary characteristic. Moreover, he states that the available evidence suggests that genes are uni-molecular, and he notes:

If a gene is a complex organic molecule it would be expected to be similar in composition to other complex molecules, viz. molecular groups constituting this molecule (whatever these groups may be) would he arranged in chains and side chains. He then offers a drawing of the structure of DNA (!) as an example of a complex organic molecule, but is quick to add that The diagram is not intended to give any implication as to the number, the type, or the arrangement of the molecules in a gene group. Its purpose is to illustrate the molecular structure of a complex organic molecule.

Another 20 years would have to pass before the true chemical nature of the gene would be established.


Dobzhansky, T. 1930. Translocations involving the third and the fourth chromosomes of Drosophila melanogaster Genetics, 15: 347-399.

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Dobzhansky, Th. 1937. Further Data on the Variation of the Y Chromosome in Drosophila Pseudoobscura Genetics, 22: 340-346.

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Dobzhansky, Th. and Beadle, G. W. 1936. Studies on Hybrid Sterility IV. Transplanted Testes in Drosophila Pseudoobscura Genetics, 21: 832-840.

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Dobzhansky, Th. and Queal, M. L. 1938. Genetics of Natural Populations. I. Chromosome Variation in Populations of Drosophila Pseudoobscura Inhabiting Isolated Mountain Ranges Genetics, 23: 239-251.

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Dobzhansky, Th. and Sturtevant, A. H. 1938. Inversions in the Chromosomes of Drosophila Pseudoobscura Genetics, 23: 28-64.

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Dobzhansky, Th. 1935. Drosophila Miranda, a New Species Genetics, 20: 377-391.

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Dobzhansky, Th. 1935. The Y Chromosome of Drosophila Pseudoobscura Genetics, 20: 366-376.

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Dobzhansky, Th. 1936. Studies on Hybrid Sterility. II. Localization of Sterility Factors in Drosophila Pseudoobscura Hybrids Genetics, 21: 113-135.

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Dobzhansky, t. 1931. Translocations Involving the Second and the fourth chromosomes of Drosophila melanogaster Genetics, 16: 629-658.

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Doncaster, L. 1911. Heredity in the Light of Recent Research. Cambridge: University Press

This is an image facsimile version of the entire 144-page original first edition.




Drinkwater, H. 1910. A Lecture on Mendelism. London: J. M. Dent & Sons.

This is an image facsimile version of the entire 48-page original first edition.

This short book was based on a lecture given by Drinkwater as one of a series known as "Science Lectures for the People." The book provides insights into the general perception (as opposed to scholarly view) of genetics very early after the field had begun.

The book also contains some nice portraits of Mendel, Bateson, and Punnett.


Dunn, L. C. 1920. Independent Genes in Mice Genetics, 5: 344-361.

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Dunn, L. C. 1920. Linkage in Mice and Rats Genetics, 5: 325-343.

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East - Morgan - Harris - Shull 1923. The Centenary of Gregor Mendel and of Francis Galton. The Scientific Monthly, 16: 225-270.

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In December of 1922, the American Society of Naturalists held a special session to honor the centenaries of the birth of Gregor Mendel and of Francis Galton. This is the collection of the four papers presented at that session and later published in the The Scientific Monthly.


East, E. M. 1916. Studies on Size Inheritance in Nicotiana Genetics, 1:164-176.

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East, E. M. 1923. Mendel and his contemporaries. The Scientific Monthly, 16: 225-237.

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In December of 1922, the American Society of Naturalists held a special session to honor the centenaries of the birth of Gregor Mendel and of Francis Galton. This is one of the four papers presented at that session and later published in the The Scientific Monthly.


East, E. M. 1929. The concept of the gene. Proceedings of the International Congress of Plant Sciences, Ithaca, New York, August 16-23, 1926, vol. 1. Menasha, WI: George Banta Publishing Co. pp 889-895.

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As classical genetics acquired more and more explanatory power, the question what is a gene? became more important. Were genes real physical entities, or merely theoretical concepts that allowed for the mathematical modelling of inheritance. This paper represents one effort to consider The concept of the gene. The paper's opening paragraph sets the tone:

Nearly fifteen years ago I attempted to defend the thesis that the Mendelian method of recording the facts of inheritance was simply a notation useful as a description of physiological facts. The argument was an elaboration of the proposition that the germ-cell unit of heredity, the gene, was an abstract, formless, characterless concept used for convenience in describing the results of breeding experiments. It was the ghost of an entity which might later be clothed with flesh, but its usefulness at the time was due to its adaptability to mathematical treatment. By postulating that the results derived from controlled matings were due to the activities of definite germ-cell units which could be manipulated arithmetically, investigators were able to formulate new experimental tests, and thus to open the way to further discovery; but these units could be given no intelligible interpretation in terms of geometry, chemistry, or physiology.

In the last paragraph, East asserts:

We arrive, therefore, at the same port from which we departed when our discussion began. The genes are units useful in concise descriptions of the phenomena of heredity. Their place of residence is the chromosomes. Their behavior brings about the observed facts of genetics. For the rest, what we know about them is merely an interpretation of crossover frequency. In terms of geometry, chemistry, physics or mechanics, we can give them no description whatever.


East, E. M. 1936. Heterosis Genetics, 21: 375-397.

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Ephrussi, Boris and Beadle, G. W. 1937. Development of Eye Colors in Drosophila: Production and Release of cn+ Substance by the Eyes of Different Eye Color Mutants Genetics, 22: 479-483.

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Ephrussi, Boris and Beadle, G. W. 1937. Development of Eye Colors in Drosophila: Transplantation Experiments on the Interaction of Vermilion with Other Eye Colors Genetics, 22: 65-75.

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Fisher, R. A. , Immer, F. R., and Tedin, Olof 1932. The Genetical Interpretation of Statistics of the Third Degree in the Study of Quantitative Inheritance Genetics, 17: 107-124.

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Fisher, R. A. 1919. The Genesis of Twins Genetics, 4: 489-499.

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Galen. 170 AD. On the Natural Faculties.

This is a full-text HTML version of the entire book.

Galen was perhaps the last significant scholar of biology before the onset of the dark ages. Although his analysis (see below) seems odd from a modern perspective, nonetheless he is addressing some of the fundamental problems of heredity and development - how does life begin and how does it grow and develop?

Let us speak then, in the first place, of Genesis, which, as we have said, results from alteration together with shaping. The seed having been cast into the womb or into the earth (for there is no difference), then, after a certain definite period, a great number of parts become constituted in the substance which is being generated; these differ as regards moisture, dryness, coldness and warmth, and in all the other qualities which naturally derive therefrom.


Galton, Francis 1889. Natural Inheritance. London: Macmillan

This is an image facsimile version of the entire 260-page original first edition.




Galton, Francis. 1898. A Diagram of Heredity. Nature, 57:293.

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Some standard textbook descriptions of early genetics give the impression that, besides Mendel, no one attempted any genetic analysis in the entire nineteenth century. This is far from the truth, with Francis Galton offering a fine refutation. Starting just a few years after Mendel (and also working with peas), Galton carried out a series of well-received studies that resulted in his "Ancestral Law of Heredity," summarized diagrammatically in this brief communication. Galton's "Law" was so firmly established in some circles, that many adherents did not accept Mendelism until 1918, when R. A. Fisher showed that Galton's Law was in fact a natural consequence of Mendelian inheritance for polygenic traits.


Garrod, Archibald E. 1902. The incidence of alkaptonuria: A study in chemical individuality. Lancet, ii:1616-1620.

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This paper is a true classic. Like Mendel's own work, this report offers insights so far ahead of its time that it, and Garrod's follow-on work, were largely neglected, until later efforts to elucidate the physiological functioning of genes led to the Nobel-prize-winning one-gene, one-enzyme hypothesis.

Less than two years after the rediscovery of Mendelism and just a few years after the word biochemistry was first coined, Garrod reports on alkaptonuria in humans and comes to the conclusion that it is inherited as a Mendelian recessive and that the occurrence of mutations (sports in the word of the time) in metabolic function should be no more surprising than inherited variations in morphology.


Garrod, Archibald. 1923. Inborn Errors of Metabolism, Second Edition. London: Henry Frowde and Hodder & Stoughton

This is a full-text PDF image facsimile version of the entire 216-page original book.

Less than two years after the rediscovery of Mendelism and just a few years after the word biochemistry was first coined, Garrod reported on alkaptonuria in humans and came to the conclusion that it was inherited as a Mendelian recessive and that the occurrence of mutations (sports in the word of the time) in metabolic function should be no more surprising than inherited variations in morphology.

In 1908, he summarized his thinking about "inborn errors of metabolism" (his term for what we would now think of as mutations in genes affecting metabolic function) in a book. An image facsimile of the second edition (1923) of that book is presented here.

Like Mendel's work, Garrod's insights were so far ahead of their time that his entire work on metabolic mutations was largely neglected, until later efforts to elucidate the physiological functioning of genes led to the Nobel-prize-winning one-gene, one-enzyme hypothesis.


Goldschmidt, Richard 1917. Crossing Over ohne Chiasmatypie? Genetics, 2:82-95.

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Haldane, J. B. S. 1934. A Mathematical Theory of Natural and Artificial Selection Part X. Some Theorems on Artificial Selection Genetics, 19: 412-429.

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Haldane, J. B. S. and Waddington, C. H. 1931. Inbreeding and Linkage Genetics, 16: 357-374.

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Hardy, G. H. 1908. Mendelian Proportions in a Mixed Population. Science, NS. XXVIII:49-50.

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Every geneticist has heard of the Hardy-Weinberg Law and of Hardy-Weinberg Equilibrium, and nearly all basic biology texts teach that G. H. Hardy played a seminal role in founding population genetics. But, what most biologists don't realize is that Hardy's total contribution to biology consisted of a single letter to the editor in Science. The letter began,

I am reluctant to intrude in a discussion concerning matters of which I have no expert knowledge, and I should have expected the very simple point which I wish to make to have been familiar to biologists. However, some remarks of Mr. Udny Yule, to which Mr. R. C. Punnett has called my attention, suggest that it may still be worth making.

With that, Hardy offered his "simple point" and then washed his hands of biology. His autobiography, A Mathematician's Apology, makes no mention of population genetics.


Harnly, Morris Henry and Ephrussi, Boris 1937. Development of Eye Colors in Drosophila: Time of Action of Body Fluid on Cinnabar Genetics, 22: 393-401.

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Harris, J. Arthur 1923. Galton and Mendel: Their contribution to genetics and their influence on biology. The Scientific Monthly, 16: 247-263.

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In December of 1922, the American Society of Naturalists held a special session to honor the centenaries of the birth of Gregor Mendel and of Francis Galton. This is one of the four papers presented at that session and later published in the The Scientific Monthly.


Hurst, C. C. 1904. Experiments with Poultry. Reports to the Evolution Committee of the Royal Society, II, 1904, pp. 131-154

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William Bateson was the first English-speaking scientist to appreciate the potential significance of Mendel's work. He and his co-workers began immediately to confirm and extend Mendel's findings. C. C. Hurst was one of Wm Bateson's early co-workers. This report to the evolution committee of the Royal Society represents one of the very first systematic investigations into Mendelism as a possible general explanation for the fundamental mechanisms of heredity.


Huxley, T. H. 1869. Nature: Aphorisms by Goethe. Nature, 1:9-11.

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A special article, written by Huxley on request for the first issue of Nature, a new publication. The article is mainly a lengthy quote from Goethe, consisting of an extended rhapsody on "Nature."


Ibsen, Heman L. 1916. Tricolor Inheritance. II. the Basset Hound Genetics, 1: 367-376.

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Ibsen, Heman L. 1916. Tricolor Inheritance. III. Tortoiseshell Cats Genetics, 1: 377-386.

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Ibsen, Heman L. 1916. Tricolor Inheritance. I. the Tricolor Series in Guinea-pigs Genetics, 1: 287-309.

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Ibsen, Heman L. 1919. Tricolor Inheritance. Iv. the Triple Allelo-morphic Series in Guinea-pigs Genetics, 4: 597-606.

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Jennings, H. S. 1923. The Numerical Relations in the Crossing Over of the Genes, with a Critical Examination of the Theory That the Genes Are Arranged in a Linear Series Genetics, 8: 393-457.

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Jones, Donald F. (ed) 1932. Proceedings of the Sixth International Congress of Genetics, Vol. I. Austin, Texas: Genetics Society of America

This is an image facsimile version of the entire 396-page original edition.

The Proceedings of the Sixth International Congress of Genetics, held in 1932, offers a glimpse into classical genetics at the height of its power and influence. Thomas Morgan, who had just received the first Nobel Prize ever awarded in genetics, served as president of the congress.

The participants list reads like a who's who of classical genetics: The three rediscovers of Mendel - Correns, de Vries, and von Tschermak - all attended the meeting. Morgan, Sturtevant, and Muller gave talks. Population genetics and the relationship of genetics to evolution was discussed by R. A. Fisher, J. B. S. Haldane, and Sewall Wright.

According to the Treasurer's Report, the total cost of the meeting was $17,583.58.


Little, C. C. 1914. A possible Mendelian explanation for a type of inheritance apparently non-Mendelian in nature Science, 40:904-906.

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Little, C. C. 1917. The Relation of Yellow Coat Color and Black-eyed White Spotting of Mice in Inheritance Genetics, 2: 433-444.

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Luria, S. E., and Delbrück, M. 1943. Mutations of bacteria from virus sensitivity to virus resistance. Genetics, 28:491-511

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This classic paper is the "fluctuation test" in which Luria and Delbrü first demonstrated the occurrence of microbial genetics. In fact, the fluctuation test must be regarded as the founding of bacterial genetics since it gave the first real proof that bacteria both possessed genes and experienced mutation. Luria and Delbrück shared the 1969 Nobel Prize with Alfred Hershey.

Luria and Delbrück were also able to use their data to calculate the actual mutation rate per bacterial cell division. Averaged across all of their experiments, this came to approximately 2.45 x 10-8. Thus, they not only proved that true genetic mutations occurred in bacteria, but also that such mutations were just as rare in bacteria as they were in higher organisms. Their work demonstrated that heritable variation in bacteria could be attributed to mechanisms similar to those in higher organisms. The previously puzzling ability of bacteria to respond rapidly and adaptively to changes in the environment could now be recognized as nothing more than the normal consequence of random gene mutation, followed by selection, in huge, rapidly reproducing populations.

Following this discovery, many researchers hurried to determine the range of true genetic mutation occurring in bacteria. Soon, such variation was detected in virtually every trait that could be studied, such as color, colony morphology, virulence (ability to infect a host), resistance to antimicrobial agents, nutritional requirements, and fermentation abilities (i.e., the ability to use different compounds as carbon sources).


Müller, F. 1869. Facts and Arguments for Darwin. London: John Murray, Albemarle Street

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Johann Friedrich Theodor Müller (March 31, 1821 – May 21, 1897), always known as Fritz, was a German biologist and physician who emigrated to southern Brazil, where he lived in and near the German community of Blumenau, Santa Catarina. There he studied the natural history of the Atlantic forest south of São Paulo, and was an early advocate of Darwinism. He lived in Brazil for the rest of his life. Müllerian mimicry is named after him.

Müller became a strong supporter of Darwin. He wrote Für Darwin in 1864, arguing that Charles Darwin's theory of evolution by natural selection was correct, and that Brazilian crustaceans and their larvae could be affected by adaptations at any growth stage. This was translated into English by W.S. Dallas as Facts and Arguments for Darwin in 1869 (Darwin sponsored the translation and publication). If Müller had a weakness it was that his writing was much less readable than that of Darwin or Wallace; both the German and English editions are hard reading indeed, which has limited the appreciation of this significant book.


Macarthur, John W. 1933. Sex-linked Genes in the Fowl Genetics, 18: 210-220.

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Malthus, T. 1798. An Essay on the Principle of Population.

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In 1798, Thomas Malthus anonymously published this Essay, outlining why the forces of population growth tend to create a "struggle for existence" (see page 14). This book had a significant influence on Darwin as he looked for mechanisms that might explain evolutionary change. The influence shows, with Chapter Three of Darwin's Origin of Species entitled "Struggle for Existence". Now, 200 years after its first publication, Malthus' work is still an interesting read.


McClintock, Barbara and Hill, Henry E. 1931. The cytological identification of the chromosome sssociated with the r-g linkage group in Zea mays Genetics, 16: 175-190.

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McClintock, Barbara 1929. A cytological and genetical study of triploid maize Genetics, 14: 180-222.

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McClintock, Barbara. 1931. The order of the genes C, Sh, and Wx in Zea mays with reference to a cytologically known point in the chromosome. PNAS, 17:485-491.

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In this paper, McClintock provides the basic genetic and cytological information necessary to understand the logic of her classic work with Harriet Creighton: A correlation of cytological and genetical crossing-over in Zea mays that appeared immediately following this paper in PNAS.


McClung, C. E. 1901. Notes on the accessory chromosome. Anatomischer Anzeiger, 20:220-226.

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In this brief paper, McClung introduces the evidence that male and female insects exhibit different chromosomal structures in their nuclei and that spermatozoa fall into two types - those that carry the "accessory chromosome" and those that do not.

Based on this analysis, McClung suggests that the presence or absence of the "accessory chromosome" in spermatozoa may determine the sex of the progeny. McClung published this short note in 1901 to alert the scientific community of his findings and to alert them to a more detailed argument that he had already submitted for publication elsewhere and that he knew would appear a year later, in McClung, C. E. 1902. The accessory chromosome - Sex determinant?. Biological Bulletin, 3:43-84.


McClung, C. E. 1902. The accessory chromosome - Sex determinant? Biological Bulletin, 3:43-84.

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In this paper, McClung analyzes the evidence that male and female insects exhibit different chromosomal structures in their nuclei and that spermatozoa fall into two types - those that carry the "accessory chromosome" and those that do not.

Based on this analysis, McClung offers the bold hypothesis that the presence or absence of the "accessory chromosome" in spermatozoa may determine the sex of the progeny:

A most significant fact ... is that the [accessory chromosome] is apportioned to but one half of the spermatozoa. Assuming it to be true that the chromatin is the important part of the cell in the matter of heredity, then it follows that we have two kinds of spermatozoa that differ from each other in a vital matter. We expect, therefore, to find in the offspring two sorts of individuals in approximately equal numbers. ... [Since] nothing but sexual characters ... divides the members of a species into two well-defined groups, ... we are logically forced to the conclusion that the [accessory] chromosome has some bearing upon this arrangement.

That is, McClung hypothesizes that a difference in chromosome number is the cause, not an effect, of sex determination. This paper represents the first effort to associate the determination of a particular trait with a particular chromosome.


Mendel - de Vries - Correns - Tschermak 1950. The Birth of Genetics Special supplement to the journal Genetics 35(5, pt 2): 1-48.

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To celebrate the fiftieth anniversary of the rediscovery of Mendel's work, the Genetics Society of America published this special supplement, containing translations of the original papers by the rediscovers of Mendel - Carl Correns, Erik von Tschermak, and Hugo de Vries. It also contains letters written by Mendel and sent to Carl N&aum;geli, a leading botanist.

This was the first time these key works were made available in English translation.


Mendel, Gregor 1866-1873. Gregor Mendel's letters to Carl Nägeli, 1866-1873. First published in English as: Mendel, G. 1950. Gregor Mendel's Letters to Carl Nägeli. Genetics, 35(5, pt 2): 1-29. Originally published as: Abhandlungen der Mathematisch-Physischen Klasse der Königlich Sächsischen Gesellschaft der Wissenschaften 29: 189-265, 1905. Reprinted in "Carl Correns, Gesammelte Abhandlungen zur Vererbungswissenschaft aus periodischen Schriften" 1899-1924. (Fritz V. Wettstein ed.) Berlin, Julius Springer, 1924. pp. 1237-1281.

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After his original paper on peas, Mendel published only one other paper on genetics, that one on Hieracium. These letters to Nägeli provide a rare additional glimpse into Mendel's thinking as he pursued his investigations on heredity.


Mendel, Gregor 1869. On Hieracium-hybrids obtained by artificial fertilisation. Verhandlungen des naturforschenden Vereines, Abhandlungen, Brünn, Bd. VIII für das Jahr 1869, 26-31. (Translated and reprinted as an appendix to Bateson, W. 1909. Mendel's Principles of Heredity. Cambridge University Press.)

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After his original paper on peas, Mendel published only one other paper on genetics, this one on Hieracium. Unknown to Mendel, Hieracium does not experience normal sexual fertilization, making it impossible for him to confirm the findings that he had obtained earler with peas.


Mendel, Gregor. 1865. Experiments in plant hybridization. Verhandlungen des naturforschenden Vereines in Brünn, Bd. IV für das Jahr 1865, Abhandlungen, 3-47.

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For those wishing to see and read Mendel in the original, this provides an image facsimile of the original paper as it was published in German.

This version is in Adobe PDF format, but the pages are images of the original publication, not a new type-setting of the material. This is a large file (2,142,414 bytes).


Mendel, Gregor. 1865. Experiments in plant hybridization. Verhandlungen des naturforschenden Vereines in Brünn, Bd. IV für das Jahr 1865, Abhandlungen, 3-47.

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In February and March of 1865, Gregor Mendel presented the Brünn Natural History Society in Brünn, Czechoslovakia, with the results of his investigations into the mechanisms governing inheritance in pea plants. The next year, the work was published as Mendel, Gregor. 1866. "Versuche über Pflanzen Hybriden." Verhandlungen des naturforschenden Vereines in Brünn, 4:3-47.

In this remarkable paper, Mendel laid the groundwork for later became the science of genetics. However, the work was largely ignored when it appeared and Mendel moved on to other things. He died in 1884.

His work was rediscovered at the turn of the century and its significance immediately recognized. Genetics, as a formal scientific discipline, exploded into activity in 1900.

An annotated version of Mendel's paper is also available. The annotated version contains explanatory notes throughout the document. This can be useful to those reading Mendel's paper for the first time.

For those wishing to see and read Mendel in the original, a facsimile reprint edition is available. This version is in Adobe PDF format, but the pages are images of the original publication, not a new type-setting of the material. This is a large file (2,142,414 bytes).

You may also with to visit The Mendel Web site, maintained at NETSPACE.ORG by Roger Blumberg. A MIRROR SITE of MendelWeb is maintained at the University of Washington. The site offers many additional resources for the Mendel scholar.


Metz, C. W. 1937. Small Deficiencies and the Problem of Genetic Units in the Giant Chromosomes Genetics, 22: 543-556.

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Mohr, Otto L. 1932. Genetical and cytological proof of somatic elimination of the fourth chromosome in Drosophila melanogaster Genetics, 17: 60-80.

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Morgan, L. V. 1925. Polyploidy in drosophila Melanogaster with Two Attached X Chromosomes Genetics, 10: 148-178.

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Morgan, L. V. 1933. A Closed X Chromosome in Drosophila Melanogaster Genetics, 18: 250-283.

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Morgan, L. V. 1939. A Spontaneous Somatic Exchange Between Non-homologous Chromosomes in Drosophila Melanogaster Genetics, 24: 747-752.

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Morgan, Thomas H. 1909. What are "factors" in Mendelian explanations? American Breeders Association Reports, 5:365-369.

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Although T. H. Morgan is best known for heading the genetics laboratory at Columbia University (later at Cal Tech) that essentially defined American genetics research for decades, he was initially skeptical of the facile manner in which combinations of alleged Mendelian factors were being invoked to explain all manner of heritable traits.

This paper begins with a wonderful debunking of easy explanation:

In the modern interpretation of Mendelism, facts are being transformed into factors at a rapid rate. If one factor will not explain the facts, then two are invoked; if two prove insufficient, three will sometimes work out. The superior jugglery sometimes necessary to account for the result, may blind us, if taken too naïvely, to the common-place that the results are often so excellently "explained" because the explanation was invented to explain them. We work backwards from the facts to the factors, and then, presto! explain the facts by the very factors that we invented to account for them.


Morgan, Thomas H. 1910. Chromosomes and Heredity. The American Naturalist, 44:449-496.

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Work in the laboratory of T. H. Morgan was critical in establishing that genes are real, physical entities and that they are arranged in a linear order on chromosomes. In this early, analytical paper, Morgan considers whether or not chromosomes might be carriers of the hereditary material and whether or not they might control sex determination.

Morgan's careful and logical approach is captured in his final comments on sex deteremination:

Science advances by carefully weighing all of the evidence at her command. When a decision is not warranted by the facts, experience teaches that it is wise to suspend judgment, until the evidence can be put to further test. This is the position we are in today concerning the interpretation of the mechanism that we have found by means of which sex is determined. I could, by ignoring the difficulties and by emphasizing the important discoveries that have been made, have implied that the problem of sex determination has been solved. I have tried rather to weigh the evidence, as it stands, in the spirit of the judge rather than in that of the advocate. One point at least I hope to have made evident, that we have discovered in the microscopic study of the germ cells a mechanism that is connected in some way with sex determination; and I have tried to show, also, that this mechanism accords precisely with that the experimental results seem to call for. The old view that sex is determined by external conditions is entirely disproven, and we have discovered an internal mechanism by means of which the equality of the sexes where equality exists is attained. We see how the results are automatically reached even if we can not entirely understand the details of the process. These discoveries mark a distinct advance in our study of this difficult problem.


Morgan, Thomas H. 1910. Chromosomes and heredity. The American Naturalist, 44: 449-496.

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Between 1910 and 1915, work in Morgan's lab laid the foundation of the modern chromosomal theory of heredity. This paper represents Morgan's thinking early in this process.

The opening lines of his paper captures the the issues that he then deemed important to a consideration of the mechanism of heredity:

We have come to look upon the problem of heredity as identical with the problem of development. The word heredity stands for those properties of the germ-cells that find their expression in the developing and developed organism. When we speak of the transmission of characters from parent to offspring, we are speaking metaphorically; for we now realize that it is not characters that are transmitted to the child from the body of the parent, but that the parent carries over the material common to both parent and offspring. This point of view is so generally accepted to-day that I hesitate to restate it. It will serve at least to show that in what I am about to say regarding heredity and the germ-cells I shall ignore entirely the possibility that characters first acquired by the body are transmitted to the germ. Were there sufficient evidence to establish this view, our problem would be affected in so far as that we should not only have to account for the way in which the fertilized egg produces the characters of the adult, but also for the way in which the characters of the adult modify the germ-cells. The modern literature of development and heredity is permeated through and through by two contending or contrasting views as to how the germ produces the characters of the individual. One school looks upon the egg and sperm as containing samples or particles of all the characters of the species, race, line, or even of the individual. This view I shall speak of as the particulate theory of development. The other school interprets the egg or sperm as a kind of material capable of progressing in definite ways as it passes through a series of stages that we call its development. I shall call this view the theory of physico-chemical reaction, or briefly the reaction theory.


Morgan, Thomas H. 1910. Sex-limited inheritance in Drosophila. Science, 32:120-122.

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After Mendel's work was rediscovered in 1900, many researchers worked to confirm and extend his findings. Although a possible relationship between genes and chromosomes was suggested almost immediately, proof of that relationship, or even evidence that genes were physical objects, remained elusive. To many, the gene served only as a theoretical construct, conveniently invoked to explain observed inheritance patterns. In 1909, Morgan himself published a paper in which he expressed his skepticism about the facility with which Mendelian explanations were adjusted to fit the facts.

Just one year later, however, Morgan published the results of his work on an atypical male fruit fly that appeared in his laboratory, and all this began to change. Normally Drosophila melanogaster have red eyes, but Morgan's new fly had white eyes. The inheritance pattern for this new eye-color trait suggested strongly that the gene for eye-color was physically attached to the X-chromosome. In the paper, Morgan concluded:

It now becomes evident why we found it necessary to assume a coupling of [the eye-color gene] and X in one of the spermatozoa of the red-eyed F1 hybrid. The fact is that this R and X are combined, and have never existed apart.

In this present paper, Morgan offered the first evidence that genes are real, physical objects, located on chromosomes, with properties that could be manipulated and studied experimentally. The white-eyed fly provided the foundation upon which Morgan and his students established the modern theory of the gene.


Morgan, Thomas H. 1911. Chromosomes and associative inheritance. Science, New Series, 34:636-638.

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Morgan, Thomas H. 1911. Random segregation versus coupling in Mendelian inheritance Science, 34:384.

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Morgan, Thomas H. 1911. The origin of five mutations in eye color in Drosophila and their modes of inheritance. Science, New Series, 33:534-537.

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Morgan, Thomas H. 1911. The origin of nine wing mutations in Drosophila. Science, New Series, 33:496-499.

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Morgan, Thomas H. 1912. Complete linkage in the second chromosome of the male of Drosophila Science, 36:933-934.

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Morgan, Thomas H. 1913. Factors and Unit Characters in Mendelian Heredity. The American Naturalist, 47:5-16.

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Morgan, Thomas H. 1913. Simplicity versus adequacy in Mendelian formulae The American Naturalist, 47:372-374

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Soon after Mendel was rediscovered, the nature of the gene was being worked out. Along the way, many suggested changes to the symbology being used (e.g., B for dominant allele, b for recessive). Here Morgan offers some thoughts on changing Mendelian symbols.


Morgan, Thomas H. 1915. The Constitution of the Hereditary Material. Proceedings of the American Philosophical Society, 54:143-153.

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Morgan, Thomas H. 1917. The Theory of the Gene. The American Naturalist, 51:513-544.

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Morgan, Thomas H. 1919. The Physical Basis of Heredity. Philadelphia: J. B. Lippincott Company

This is a full-text PDF image facsimile version of the entire 305-page original book.

In this book, T. H. Morgan (who would later receive the first Nobel Prize for genetics research) describes the model of heredity developed at Columbia by Morgan and his students.

The foundations of genetics were laid down by Mendel, and these were brought to the world's attention when his work was resdiscovered by Correns, de Vries, and von Tschermak in 1900. But the real establishment of genetics as a real science, with a known physical basis, did not occur until the work outlined in this book became generally known.

To understand the true conceptual underpinnings of classical genetics, one must read the publications from "The Fly Room" at Columbia.


Morgan, Thomas H. 1922. Croonian Lecture: On the Mechanism of Heredity. Proceedings of the Royal Society, B, 94:162-197.

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The Croonian Lecture is the Royal Society's premier lecture in the biological sciences. Dr Croone, one of the original members of the Society, left on his death in 1684 a scheme for two lectureships, one at the Royal Society and the other at the Royal College of Physicians

Morgan was invited to give the Croonian lecture in 1922 - a recognition of his pioneering work in elucidating the physical basis of heredity.


Morgan, Thomas H. 1923. The bearing of Mendelism on the origin of species. The Scientific Monthly, 16: 237-247.

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In December of 1922, the American Society of Naturalists held a special session to honor the centenaries of the birth of Gregor Mendel and of Francis Galton. This is one of the four papers presented at that session and later published in the The Scientific Monthly.


Morgan, Thomas H. 1928. The Theory of the Gene, Revised and Enlarged Edition. New Haven: Yale University Press

This is a full-text PDF image facsimile version of the entire 358-page original book.

This book, by T. H. Morgan, summarizes the state of knowledge on classical genetics in the mid 1920's.

Although Mendelism had quickly been accepted as a good phenomenological explanation for the patterns seen in Mendelian crosses, until the work of Morgan's group, it was still possible to consider Mendelism to be a purely theoretical model of heredity. As Morgan's group first established the relationship of genes to chromosomes, then developed the first genetic map, and went on to describe a variety of interactions between chromosomes and Mendelian factors, the conclusions they offered became inescapable – genes are physical objects, carried on chromosomes in static locations.

Less than 15 years after Morgan first started working with fruit flies, the foundations for a theory of the gene had been worked out – largely by Morgan and students working in his laboratory.


Morgan, Thomas H., Sturtevant, A. H., Muller, H. J., and C. B. Bridges 1915. The Mechanism of Mendelian Heredity. New York: Henry Holt and Company

This is a full-text PDF image facsimile version of the entire 262-page original book.

This book, by T. H. Morgan and his students, is the first work to articulate a comprehensive, mechanistic model to explain Mendelian patterns of inheritance.

Although Mendelism had quickly been accepted as a good phenomenological explanation for the patterns seen in Mendelian crosses, until the work of Morgan's group, it was still possible to consider Mendelism to be a purely theoretical model of heredity. As Morgan's group first established the relationship of genes to chromosomes, then developed the first genetic map, and went on to describe a variety of interactions between chromosomes and Mendelian factors, the conclusions they offered became inescapable - genes are physical objects, carried on chromosomes in static locations.

Morgan's group made genes real and this book is the first full-length presentation of their findings. It revolutionized the study of heredity.


Morgan, Thomas Hunt 1897. The Development of the Frog's Egg: An Introduction to Experimental Embryology. New York: The Macmillan Company

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Thomas Hunt Morgan is best known for his work in genetics, for which he received the Nobel Prize in 1933. Morgan's first research interest, however, was in embryology. This short book on frog development is his first book.

From the Preface: The development of the frog's egg was first made known through the studies of Swammerdam, Spallanzani, Rusconi, and von Baer. Their work laid the basis for all later research. More recently the experiments of Pfluger and of Roux on this egg have turned the attention of embryologists to the study of development from an experimental standpoint. Owing to the ease with which the frog's egg can be obtained, and its tenacity of life in a confined space, as well as its suitability for experimental work, it is an admirable subject with which to begin the study of vertebrate development. In the following pages an attempt is made to bring together the most important results of studies of the development of the frog's egg. I have attempted to give a continuous account of the development, as far as that is possible, from the time when the egg is forming to the moment when the young tadpole issues from the jelly-membranes. Especial weight has been laid on the results of experimental work, in the belief that the evidence from this source is the most instructive for an interpretation of the development. The evidence from the study of the normal development has, however, not been neglected, and wherever it has been possible I have attempted to combine the results of experiment and of observation, with the hope of more fully elucidating the changes that take place. Occasionally departures have been made from the immediate subject in hand in order to consider the results of other work having a close bearing on the problem under discussion. I have done this in the hope of pointing out more definite conclusions than could be drawn from the evidence of the frog's egg alone.


Muller, H. J. and Jacobs-muller, Jessie M. 1925. The Standard Errors of Chromosome Distances and Coincidence Genetics, 10: 509-524.

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Muller, H. J., Raffel, D., Gershenson, S. M. , and Prokofyeva-Belgovskaya, A. A. 1937. A Further Analysis of Loci in the So-called "inert Region" of the X Chromosome of Drosophila Genetics, 22: 87-93.

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Muller, Hermann J. 1916. The Mechanism of Crossing-over. New York: The American Naturalist

This is an image facsimile version of the entire 86-page original edition.

Beginning 1910, T. H. Morgan and his students established the foundations of modern genetics by making genes real - not theoretical entities.

This work is a collection of papers that represented the doctoral dissertation of one of those students - H. J. Muller.


Muller, Hermann J. 1918. Genetic Variability, Twin Hybrids and Constant Hybrids, in a Case of Balanced Lethal Factors Genetics, 3: 422-499.

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Muller, Hermann J. 1918. Genetic variability, twin hybrids and constant hybrids, in a case of balanced lethal factors.. Genetics, 3:422-499.

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Muller, Hermann J. 1922. Variation due to change in the individual gene. The American Naturalist, 56:32-50.

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This paper is from an address given by to the thirty-ninth annual meeting of the American Society of Naturalists, held in Toronto on 29 December 29 1921.

In this remarkably prescient analysis, Muller lays out the paradoxical nature of the genetic material. It is apparently both autocatalytic (i.e., directs its own synthesis) and heterocatalytic (i.e., directs the sythesis of other molecules), yet only the heterocatalytic function seems subject to mutation. With this, he defines the key problems that must be solved for a successful chemical model of the gene.

Muller also anticipated the ultimate development of molecular genetics:

That two distinct kinds of substances -- the d'Hérelle substances (NOTE: viruses) and the genes -- should both possess this most remarkable property of heritable variation or "mutability," each working by a totally different mechanism, is quite conceivable, considering the complexity of protoplasm, yet it would seem a curious coincidence indeed. It would open up the possibility of two totally different kinds of life, working by different mechanisms. On the other hand, if these d'Hérelle bodies were really genes, fundamentally like our chromosome genes, they would give us an utterly new angle from which to attack the gene problem. They are filterable, to some extent isoluble, can be handled in test tubes, and their properties, as shown by their effects on the bacteria, can then be studied after treatment. It would be very rash to call these bodies genes, and yet at present we must confess that there is no distinction known between the genes and them. Hence we cannot categorically deny that perhaps we may be able to grind genes in a mortar and cook them in a beaker after all. Must we geneticists become bacteriologists, physiological chemists and physicists, simultaneously with being zoologists and botanists? Let us hope so.


Muller, Hermann J. 1925. The regionally differential effect of X rays on crossing over in autosomes of Drosophila. Genetics, 10:470-507.

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Muller, Hermann J. 1927. Artificial transmutation of the gene. Science, 46:84-87.

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Muller, Hermann J. 1928. The measurement of gene mutation rate in Drosophila, its high variability, and its dependence upon temperature. Genetics, 13:279-357.

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Muller, Hermann J., Raffel, D., Gershenson, S. M., and Prokofya-Belgovskaya, A. A. 1937. A further analysis of loci in the so-called "inert region" of the X chromosome of Drosophila. Genetics, 22:87-93.

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Muller, Hermann J., and Altenburg, Edgar. 1930. The frequency of translocations produced by X-rays in Drosophila. Genetics, 15:283-311.

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Muller, Hermann J., and Jacobs-Muller, Jessie M. 1925. The standard errors of chromosome distances and coincidence. Genetics, 10:509-524.

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Painter, Theophilus S. 1928. A Comparison of the Chromosomes of the Rat and Mouse with Reference to the Question of Chromosome Homology in Mammals Genetics, 13: 180-189.

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Painter, Theophilus S. 1935. The Morphology of the Third Chromosome in the Salivary Gland of Drosophila Melanogaster and a New Cytological Map of this Element Genetics, 20: 301-326.

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Painter, Theophilus S. and Griffen, Allen B. 1937. The Structure and the Development of the Salivary Gland Chromosomes of Simulium Genetics, 22: 612-633.

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Painter, Theophilus S. and Stone, Wilson 1935. Chromosome Fusion and Speciation in Drosophilae Genetics, 20: 327-341.

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Painter, Theophilus S. 1934. A New Method For the Study of Chromosome Aberrations and the Plotting of Chromosome Maps in Drosophila melanogaster. Genetics, 19: 175-188.

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Now, almost any reference to the genetics of Drosophila includes some illustration of the giant salivary gland chromosomes found in these flies. Although Drosophila had been used effectively since 1910, it was this paper by Painter that first showed the tremendous potential of these chromosomes for cytogenetic research. New discovery often hinges on new methods and this paper is truly a break-through study in genetic methodology.


Painter, Theophilus S. 1934. The Morphology of the X Chromosome in Salivary Glands of Drosophila melanogaster and a New Type of Chromosome Map for this Element. Genetics, 19: 448-469.

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In this paper, Painter follows up on his earlier publication describing Drosophila giant salivary-gland chromosomes and here shows how genetics maps, obtained from crossing studies, can be placed on a morphological map obtained from cytological studies.


Patterson, J. T. and Muller, H. J. 1930. Are "progressive" mutations produced by X-rays? Genetics, 15: 495-577.

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Patterson, J. T. 1933. The Mechanism of Mosaic Formation in Drosophila Genetics, 18: 32-52.

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Payne, F. 1924. Crossover Modifiers in the Third Chromosome of Drosophila melanogaster Genetics, 9: 327-342.

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Plough, Harold H. and Ives, Philip T. 1935. Induction of Mutations by High Temperature in Drosophila Genetics, 20: 42-69.

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Punnett, R. C. 1905. Mendelism, 1st Edition. Cambridge: Bowes and Bowes

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This little book is the first edition of the first genetics textbook ever written. It was published just five years after Mendel's work was rediscovered.


Punnett, R. C. 1907. Mendelism, 2nd Edition. Cambridge: Bowes and Bowes

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This second edition of Punnett's text on Mendelism came out just two years after the first edition. In this new edition, Punnett Squares appeared for the first time. Also, the author included an index (that could fit on a single page with room left over).


Rhoades, Marcus M. 1933. An Experimental and Theoretical Study of Chromatid Crossing Over Genetics, 18: 535-555.

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Riddle, Oscar. 1924. Any Hereditary Character and the Kinds of Things We Need to Know About It. The American Naturalist, LVIII:410-425.

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This does not qualify as a classic genetics paper and I suspect that it has never before been included in a collection of important papers. However, it is included here because it provides a glimpse into some general aspects of genetic thought in the mid 1920's.

The premise of this essay is essentially that, as of its writing, " studies on heredity and evolution offer what is mainly a two-sided attack on a many-sided problem." This argument was well taken, but the modern reader may have difficulty appreciating other concerns of the essay.


Schultz, Jack 1929. The minute reaction in the development of Drosophila melanogaster Genetics, 14: 366-419.

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Schultz, Jack 1933. X-ray Effects on Drosophila Pseudo-obscura Genetics, 18: 284-291.

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Schultz, Jack, and Dobzhansky, Th. 1934. The Relation of a Dominant Eye Color in Drosophila Melanogaster to the Associated Chromosome Rearrangement Genetics, 19: 344-364.

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Shull, A. Franklin 1922. Ten Years of Heredity. Transactions of the American Microscopical Society, 41:82-100.

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Shull, G. H. 1915. Genetic Definitions in the New Standard Dictionary. The American Naturalist, 49:52-59.

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In this short paper, Shull takes exception to some recently published dictionary definitions of many technical genetics terms and he offers corrected definitions in their stead. The main value of this paper to modern readers is that it gives a very good idea of what geneticists (or at least this geneticist) meant by their use of genetic terminology at the time. Although many of Shull's proffered definitions would be at home in a modern biology text, some are no longer in current usage.

Shull could have done a better job of defining "alternative inheritance" by adding "contrast with continuous inheritance," since at the time of his writing there was still a school of thought that argued that most heritable variation was continuous but that Mendelian theories provided explanations only for cases of "alternative inheritance," which were rare in nature and might only represent artifacts of inheritance in domesticated organisms.

For just such a criticism of alternative inheritance, see Weldon, W. F. R. 1902 Mendel's laws of alternative inheritance in peas. Biometrika, 1:228-254, soon to be republished by the Electronic Scholarly Publishing project.


Shull, George H. 1923. A permanent memorial to Galton and Mendel. The Scientific Monthly, 16: 263-270.

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In December of 1922, the American Society of Naturalists held a special session to honor the centenaries of the birth of Gregor Mendel and of Francis Galton. This is one of the four papers presented at that session and later published in the The Scientific Monthly.


Shull, George Harrison 1909. The "Presence and Absence" Hypothesis. The American Naturalist, 43:410-419.

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Sivertzev-Dobzhansky, N. P. and Dobzhansky, Th. 1933. Deficiency and Duplications For the Gene Bobbed in Drosophila Melanogaster Genetics, 18: 413.

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Snyder, Laurence H. 1924. The Inheritance of the Blood Groups Genetics, 9: 465-478.

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Snyder, Laurence H. 1934. Studies in Human Inheritance. X. a Table to Determine the Proportion of Recessives to Be Expected in Various Matings Involving a Unit Character Genetics, 19: 1-17.

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Stadler, L. J. 1926. The Variability of Crossing Over in Maize Genetics, 11: 1-37.

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Stern, Curt and Bridges, Calvin B. 1926. The Mutants of the Extreme Left End of the Second Chromosome of Drosophila melanogaster Genetics, 11: 503-530.

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Stevens, Nettie M. 1905. Studies in Spermatogenesis with especial reference to the "accessory chromosome". Carnegie Institution of Washington, Publication No. 36., pp 1-33.

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Stevens, Nettie M. 1906. Studies in Spermatogenesis Part II., A comparative study of the heterochromosomes in certain species of coleoptera, hemiptera and lepidoptera, with especial reference to sex determination. Carnegie Institution of Washington, Publication No. 36, part II., pp 1-43.

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Stevens, Nettie M. 1906. Studies on the germ cells of aphids. Carnegie Institution of Washington, Publication No. 51., pp 1-28.

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Sturtevant, A. H. and Beadle, G. W. 1936. The Relations of Inversions in the X Chromosome of Drosophila Melanogaster to Crossing Over and Disjunction Genetics, 21: 554-604.

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Sturtevant, A. H. and Dobzhansky, Th. 1936. Geographical Distribution and Cytology of "sex Ratio" in Drosophila Pseudoobscura and Related Species Genetics, 21: 473-490.

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Sturtevant, A. H. 1917. Crossing Over without Chiasmatype? Genetics, 2:301-304.

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Sturtevant, A. H. 1936. Preferential Segregation in Triplo-IV Females of Drosophila Melanogaster Genetics, 21: 444-466.

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Sturtevant, A. H., Bridges, C. B., and Morgan, T. H. 1919. The spatial relations of genes. Proceedings of the National Academy of Sciences, 5:168-173.

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Sturtevant, Alfred H. 1965. A History of Genetics. First published in 1965, it was brought back into print in 2001 by Cold Spring Harbor Laboratory Press and the Electronic Scholarly Publishing project.

This is a full-text PDF typeset version of the entire 167-page original book.

Between 1910 and 1915, the modern chromosomal theory of heredity was established, largely through work done in the laboratory of Thomas H. Morgan at Columbia University. This book, by one of Morgan's students, presents the history of early genetics and captures the excitement as a new discipline was being born.

Sturtevant himself made major contributions to genetics, including the development of the world's first genetic map in 1913.


Sturtevant, Alfred H. 1913. The linear arrangement of six sex-linked factors in Drosophila, as shown by their mode of association. Journal of Experimental Biology, 14:43-59.

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In 1998, with genome projects routinely producing detailed genetics maps of mice and men and every other sort of organism, it can be difficult to imagine a time when there were no genetic maps. The idea that individual genes occupy regular positions on chromosomes was one of the great insights of early genetics, and the very first genetic map was published in 1913 by Alfred H. Sturtevant, who was working on fruit flies in the laboratory of Thomas H. Morgan at Columbia University.

Sturtevant is now well known as one of the most important early pioneers in genetic research. However, at the time he produced the first map, he was an undergraduate. Many years later, Sturtevant (A History of Genetics) described how an undergraduate came to be crucially involved in establishing the very foundations of classical genetics:

In 1909, the only time during his twenty-four years at Columbia, Morgan gave the opening lectures in the undergraduate course in beginning zoology. It so happened that C. B. Bridges and I were both in the class. While genetics was not mentioned, we were both attracted to Morgan and were fortunate enough, though both still undergraduates, to be given desks in his laboratory the following year (1910-1911). The possibilities of the genetic study of Drosophila were then just beginning to be apparent; we were at the right place at the right time. In the latter part of 1911, in conversation with Morgan, I suddenly realized that the variations in strength of linkage, already attributed by Morgan to differences in the spatial separation of the genes, offered the possibility of determining sequences in the linear dimension of a chromosome. I went home and spent most of the night (to the neglect of my undergraduate homework) in producing the first chromosome map, which included the sex-linked genes y, w, v, m, and r, in the order and approximately the relative spacing that they still appear on the standard maps (Sturtevant, 1913).


Sturtevant, Alfred H. 1920. Genetic studies on Drosophila simulans. I. Introduction. Hybrids with Drosophila melanogaster. Genetics, 5:488-500.

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Sturtevant, Alfred H. 1921. Genetic studies on Drosophila simulans. II. Sex-linked groups of genes. Genetics, 6:43-64.

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Sturtevant, Alfred H. 1921. Genetic studies on Drosophila simulans. III. Autosomal genes. General discussion. Genetics, 6:179-207.

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Sturtevant, Alfred H. 1923. Inheritance of the direction of coiling in Limnaea. Science, 58:269-270.

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As evidence mounted for the chromosomal basis of inheritance, occasional examples were discovered that seemed to challenge the Mendelian model, as mapped to the chromosomes by T. H, Morgan and his students. In this paper, A. H. Sturtevant (one of Morgan’s students) shows that apparently aberrant patterns of inheritance can be seen to correspond to the Mendelian model, if care is taken to assign phenotype to the correct individual.

The case in question is the direction of shell coiling in snails of the genus Limnaea. These shells can either coil to the right (dextral) or left (sinistral). Coiling seemed to be an inherited trait, except that the observed patterns of inheritance were strange. Broods of offspring from sinistral snails, produced by self-fertilization (these snails are hermaphroditic) were either all sinistral or all dextral (never some of each). The same was found true if the single parent was dextral. Complicated models had been offered to explain these results, but here Sturtevant shows that a much simpler model is equally effective:

An analysis ?£ the data presented suggests that the case is a simple Mendelian one, with the dextral character dominant, but with the nature of a given individual determined, not by its own constitution but by that of the unreduced egg from which it arose.

A similar problem exists with the color of bird eggs. Chickens, for example, can produce eggs that are either brown or white, and these colors are genetically determined. However, the trait “shell color” is an attribute of the hen laying the eggs, not of the chick that hatches out of the egg. When you realize that the shell is created as a secretion in the hen’s oviducts, this makes perfect sense, even though the actual egg shell is ultimately separate from the body of the hen and is part of the egg from which the chick hatches.

The direction of shell coiling is now known to be controlled by specific proteins present in the cytoplasm of the egg. These proteins are produced early in egg development, prior to fertilization, and so are produced solely from genes present in the mother. Just as with the color of egg shells in chickens, the direction of shell coiling in Limnaea is really part of the phenotype of the mother of the snail, not of the snail actually wearing the shell.


Sturtevant, Alfred H. 1925. The effects of unequal crossing over at the bar locus in Drosophila. Genetics, 10:117-147.

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Sturtevant, Alfred H. 1928. A further study of the so-called mutation at the bar locus of Drosophila. Genetics, 13:401-409.

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Sutton, Walter S. 1902. On the morphology of the chromosome group in Brachystola magna. Biological Bulletin, 4:24-39.

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In this paper, Sutton reports cytological studies of grasshopper chromosomes that lead him to conclude that (a) chromosomes have individuality, (b) that they occur in pairs, with one member of each pair contributed by each parent, and (c) that the paired chromosomes separate from each other during meiosis.

After presenting considerable evidence for his assertions, Sutton closes his paper with a sly reference to its undoubted significance:

I may finally call attention to the probability that the association of paternal and maternal chromosomes in pairs and their subsequent separation during the reducing division as indicated above may constitute the physical basis of the Mendelian law of heredity. To this subject I hope soon to return in another place.


Sutton, Walter S. 1903. The chromosomes in heredity. Biological Bulletin, 4: 231-251.

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Early on, some researchers noticed that Mendel's theory required that some kind of hereditary unit segregate in pairs to offspring. Sutton was one of the first to note that the chromosomes behaved in exactly a manner to match this requirement.

The opening lines of his paper show that he is aware of the significance of his observations:

In a recent announcement of some results of a critical study of the chromosomes in the various cell generations of Brachystola the author briefly called attention to a possible relation between the phenomena there described and certain conclusions first drawn from observations on plant hybrids by Gregor Mendel in 1865, and recently confirmed by a number of able investigators. Further attention has already been called to the theoretical aspects of the subject in a brief communication by Professor E. B. Wilson. The present paper is devoted to a more detailed discussion of these aspects, the speculative character of which may be justified by the attempt to indicate certain lines of work calculated to test the validity of the conclusions drawn. The general conceptions here advanced were evolved purely from cytological data, before the author had knowledge of the Mendelian principles, and are now presented as the contribution of a cytologist who can make no pretensions to complete familiarity with the results of experimental studies on heredity. As will appear hereafter, they completely satisfy the conditions in typical Mendelian cases, and it seems that many of the known deviations from the Mendelian type may be explained by easily conceivable variations from the normal chromosomic processes.


Taliaferro, W. H., and Huck, J. G. 1923. The Inheritance of Sickle-cell Anaemia in Man Genetics, 8: 594-598.

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Tan, C. C. 1936. Genetic Maps of the Autosomes in Drosophila Pseudoobscura Genetics, 21: 796-807.

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Thomson, J. Arthur. 1908. Heredity. London: John Murray

This is a PDF image facsimile version of the entire 596-page original first edition.

This book is one of the first textbook treatments of heredity after the rediscovery of Mendel's work. Thomson provides his analysis in the context of the understanding of inheritance in the pre-Mendelian late nineteenth century. Chapter 11, History of Theories of Heredity and Inheritance summarizes many of the nineteenth-century theories of heredity.

In his bibliography, Thomson cites many nineteenth-century works. He also provides a subject-index to the bibliography, making this collection of citations especially valuable.


Tschermak, Erik von 1900. Concerning artificial crossing in Pisum sativum First published in English as: Tschermak, E. 1950. Concerning artificial crossing in Pisum sativum. Genetics, 35(5, pt 2): 42-47. Originally published as: Tschermak, E. 1900. Über Künstliche Kreuzung bei Pisum sativum. Berichte der Deutsche Botanischen Gesellschaft 18: 232-239, 1900.

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Tschermak, along with Carl Corren and Hugo de Vries, is considered to be one of the three co-discovers of Mendel's work in 1900. He had been working himself with garden peas when he rediscovered Mendel's prior contributions. In a postscript to his paper, he wrote:

Correns has just published experiments which also deal with artificial hybridization of different varieties of Pisum sativum and observations of the hybrids left to self-fertilization through several generations. They confirm, just as my own, Mendel's teachings. The simultaneous "discovery" of Mendel by Correns, de Vries, and myself appears to me especially gratifying. Even in the second year of experimentation, I too still believed that I had found something new.


Vries, Hugo De 1925. Mutant Races Derived from oenothera Lamarckiana Semigigas Genetics, 10: 211-222.

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Vries, Hugo de 1900. Concerning the law of segregation of hybrids. First published in English as: De Vries, H.. 1950. Concerning the law of segregation of hybrids. Genetics, 35(5, pt 2): 30-32. Originally published as: De Vries, H. 1900. Sur la loi de disjonction des hybrides. Comptes Rendus de l'Academie des Sciences (Paris), 130: 845-847.

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Hugo de Vries, along with Carl Correns and Erik von Tschermak, is considered to be one of the three co-discovers of Mendel's work in 1900. De Vries was by far the most established scientist at the time, with an established research record dealing with "mutations" (variations) and speciation.

In this first of two papers that he published in 1900, de Vries does not even mention Mendel by name, even though he adopts Mendelian terminology such as dominant and recessive.


Vries, Hugo de 1918. Mutations of Oenothera suaveolens desf. Genetics, 3:1-26.

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Vries, Hugo de 1918. Twin hybrids of Oenothera hookeri T. and G.. Genetics, 3:397-421.

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Vries, Hugo de 1925. Mutant races derived from Oenothera lamarckiana semigigas. Genetics, 10:211-222.

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Vries, Hugo de, and Boedijn, K. 1923. On the distribution of mutant characters among the chromosomes of Oenothera lamarckiana. Genetics, 8:233-238.

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Vries, Hugo de. 1910. Intracellular Pangenesis. Chicago: The Open Court Publishing Co.

This is a full-text PDF image facsimile version of the entire 270-page original book

This classic work, first published in German in 1889, presents De Vries's theory of the pangen, a morphological structure carrying hereditary material. The name "gene," later coined by Johannsen, was derived from de Vries's pangen.

Hugo De Vries is often now remembered, along with Correns and von Tschermak, primarily for their role in the rediscovery of Mendel in 1900. Of the three, however, De Vries was by far the most established scientist. He was one of the most well-known botanists in Europe and had already been developing his own theoretical model of heredity - intracellular pangenesis.

Intracellular pangenesis was based on Darwins's concept of pangenesis as presented in chapter 27 of his massive, two-volume The Variation of Animals and Plants under Domestication. De Vries view, however, has a more modern feel than Darwin's, as De Vries thought about the inheritance of individual characters (as did Mendel), not just about more general overall species characteristics. De Vries called his units of inheritance pangens and later he came to believe that a pangen for a particular trait was the same, no matter in which species it occurred. This is an interesting anticipation of what would later be seen as genetic homology.


Wallace. A. R. 1855. On the law which has regulated the introduction of new species. Annals and Magazine of Natural History, 2nd Series. 16:184-196.

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Today Darwin's name is known to everyone, while Alfred Russel Wallace is familiar to only a few. Yet the concept of evolution by natural selection was independently developed by Wallace and Darwin, with Wallace publishing first. This paper, and the 1858 manuscript he sent directly to Darwin, show clearly that, prior to Darwin's publication, Wallace had a firm grasp on the concept of evolution.


Weinberg, Wilhelm 1908. Über Vererbungsgesetze beim Menschen. Zeitschrift für Induktive Abstammungs- und Vererbungslehre, 1:377-392.

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An early contribution from Weinberg on the study of inheritance in humans.


Weinstein, Alexander 1936. The Theory of Multiple-strand Crossing Over Genetics, 21: 490.

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Weinstein, Alexander 1936. The Theory of Multiple-strand Crossing Over Genetics, 21: 155-199.

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Weinstein, Alexander 1918. Coincidence of Crossing Over in drosophila Melanogaster (ampelophila) Genetics, 3: 135-172.

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Weismann, August 1889. Essays Upon Heredity. Oxford at the Clarendon Press

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August Weismann was one of the most influential biologists of the late nineteenth century. In Essays Upon Heredity he presents a series of essays giving his thoughts on the mechanisms of heredity. Two of the essays offer specific refutation of the idea that acquired characters can be inherited.


Weismann, August 1893. The Germ-Plasm. New York: Charles Scribner's Sons

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August Weismann was one of the most influential biologists of the late nineteenth century. In The Germ-Plasm he lays out a new theory of heredity, one based on the continuity of the germ-plasm (the gametes and the cells that give rise to the gametes) as opposed to the finite existence of the soma (the cells of the body).

Weismann introduces his book modestly:

Any attempt at the present time to work out a theory of heredity in detail may appear to many premature, and almost presumptuous: I confess there have been times when it has seemed so even to myself. I could not, however, resist the temptation to endeavour to penetrate the mystery of this most marvellous and complex chapter of life as far as my own ability and the present state of our knowledge permitted.

A key point in his theory is that it makes impossible the inheritance of acquired characteristics, and thus deals a death blow to Lamarckism, as well as to Darwin's pangenesis:

What first struck me when I began seriously to consider the problem of heredity, some ten years ago, was the necessity for assuming the existence of a special organised and living hereditary substance, which in all multicellular organisms, unlike the substance composing the perishable body of the individual, is transmitted from generation to generation. This is the theory of the continuity of the germ-plasm. My conclusions led me to doubt the usually accepted view of the transmission of variations acquired by the body (soma); and further research, combined with experiments, tended more and more to strengthen my conviction that in point of fact no such transmission occurs.


Weldon, W. F. R. 1902. Mendel's laws of alternative inheritance in peas. Biometrika, 1:228-254.

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Textbook treatments of genetics often give the impression that upon being rediscovered Mendel's dominated the field. This is not so. Galton and his followers had been working for decades studying patterns of inheritance and had developed a formal quantitative model for the inheritance of "natural" (i.e., continuous) traits.

The biometricians, as they were called, felt that Mendel's work was a limited assessment, valid only when applied to discontinuous traits in domesticated species. Weldon was a leading proponent of the biometrician school. This paper provides a strong summary of why the biometricians believed Mendel's work to be fundamentally flawed and of no general consequence. The paper concludes:

The fundamental mistake which vitiates all work based upon Mendel's method is the neglect of ancestry, and the attempt to regard the whole effect upon offspring, produced by a particular parent, as due to the existence in the parent of particular structural characters; while the contradictory results obtained by those who have observed the offspring of parents apparently identical in certain characters show clearly enough that not only the parents themselves, but their race, that is their ancestry, must be taken into account before the result of pairing them can be predicted.


Wilson, Edmund B. 1900. The Cell in Development and Inheritance, 2nd Edition New York: The Macmillan Company

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Edmund B. Wilson was the leading cytologist of his time and The Cell in Development and Inheritance was the definitive text on cytology from 1896 into the 1930's. A modern reader will be surprised to see how many of the illustrations in the book seem familiar – versions of many of them still appear in textbooks of introductory biology.

The last chapter in the book is entitled "Theories of Inheritance and Development:, and it begins:

Every discussion of inheritance and development must take as its point of departure the fact that the germ is a single cell similar in its essential nature to any one of the tissue-cells of which the body is composed. That a cell can carry with it the sum total of the heritage of the species, that it can in the course of a few days or weeks give rise to a mollusk or a man, is the greatest marvel of biological science. In attempting to analyze the problems that it involves, we must from the outset hold fast to the fact, on which Huxley insisted, that the wonderful formative energy of the germ is not impressed upon it from without, but is inherent in the egg as a heritage from the parental life of which it was originally a part. The development of the embryo is nothing new. It involves no breach of continuity, and is but a continuation of the vital processes going on in the parental body. What gives development its marvellous character is the rapidity with which it proceeds and the diversity of the results attained in a span so brief.

But when we have grasped this cardinal fact, we have but focussed our instruments for a study of the real problem. How do the adult characteristics lie latent in the germ-cell; and how do they become patent as development proceeds? This is the final question that looms in the background of every investigation of the cell. In approaching it we may well make a frank confession of ignorance; for in spite of all that the microscope has revealed, we have not yet penetrated the mystery, and inheritance and development still remain in their fundamental aspects as great a riddle as they were to the Greeks. What we have gained is a tolerably precise acquaintance with the external aspects of development. The gross errors of the early preformationists have been dispelled.' We know that the germ-cell contains no predelineated embryo; that development is manifested, on the one hand, by the cleavage of the egg, on the other hand, by a process of differentiation, through which the products of cleavage gradually assume diverse forms and functions, and so accomplish a physiological division of labour. We can clearly recognize the fact that these processes fall in the same category as those that take place in the tissue-cells; for the cleavage of the ovum is a form of mitotic cell-division, while, as many eminent naturalists have perceived, differentiation is nearly related to growth and has its root in the phenomena of nutrition and metabolism. The real problem of development is the orderly sequence and correlation of these phenomena toward a typical result. We cannot escape the conclusion that this is the outcome of the organization of the germ-cells; but the nature of that which, for lack of a better term, we call "organization," is and doubtless long will remain almost wholly in the dark.


Wilson, Edmund B. 1902. Mendel's principles of heredity and the maturation of the germ cells. Science, NS 16: 991-993.

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In this short note, E. B. Wilson calls attention to the possible relationship between Mendelian patterns of inheritance and the assortment of chromosomes in meiosis.


Wilson, Edmund B. 1905. The chromosomes in relation to the determination of sex in insects. Science, N.S. 22:500-502.

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In this short note, Wilson (a leading cell biologist of his time) offers his endorsement of the idea that there is a relationship between specific chromosomes and the determination of sex in insects:

Material procured during the past summer demonstrates with great clearness that the sexes of Hemiptera show constant and characteristic differences in the chromosome groups, which are of such a nature as to leave no doubt that a definite connection of some kind between the chromosomes and the determination of sex exists in these animals. These differences are of two types. In one of these, the cells of the female possess one more chromosome than those of the male; in the other, both sexes possess the same number of chromosomes, but one of the chromosomes in the male is much smaller than the corresponding one in the female (which is in agreement with the observations of Stevens on the beetle Tenebrio).

Wilson's contribution is the observation that the various cases all seem to fall cleanly into one of two types -- those in which the male seems to be missing a chromosome, and those in which the male is carrying a pair of mis-matched chromosomes. Wilson's goes on to note that he does not believe that the 'accessory chromosomes' are actual sex determinants as conjectured by McClung, but rather that they probably act in a quantitative, not qualitative manner.

Wilson's endorsement of the idea that chromosome make-up is related to sex determination greatly facilitated the later general acceptance of the notion that individual chromosomes might be related to individual traits. Of course, sex is not a simple Mendelian trait, such as round or wrinkled peas, but nonetheless the evidence that some aspect of phenotype (sex) was related to some aspect of genotype was an important initial step in bringing genetics together with cytology.


Wilson, Edmund B. 1909. Recent researches on the determination and heredity of sex. Science, NS 29:53-70.

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Wilson, Edmund B. 1909. Secondary chromosome-couplings and the sexual relations in Abraxas. Science, NS 29:704-706.

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Wright, Sewall and Chase, Herman B. 1936. On the Genetics of the Spotted Pattern of the Guinea Pig Genetics, 21: 758-787.

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Wright, Sewall 1918. On the nature of size factors. Genetics, 3:367-374.

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Wright, Sewall 1921. Systems of mating. I. The biometric relations between parent and offspring. Genetics, 6:111-123.

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Wright, Sewall 1921. Systems of mating. II. The effects of inbreeding on the genetic composition of a population. Genetics, 6:124-143.

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Wright, Sewall 1921. Systems of mating. III. Assortative mating based on somatic resemblance. Genetics, 6:144-161.

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Wright, Sewall 1921. Systems of mating. IV. The effects of selection. Genetics, 6:162-166.

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Wright, Sewall 1921. Systems of mating. V. General considerations. Genetics, 6:167-178.

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Wright, Sewall 1925. The factors of the albino series of guinea-pigs and their effects on black and yellow pigmentation. Genetics, 10:223-260.

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Wright, Sewall 1927. The effects in combination of the major color-factors of the guinea pig Genetics, 12: 530-569.

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Wright, Sewall 1928. An eight-factor cross in the guinea pig Genetics, 13: 508-531.

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Wright, Sewall 1931. Evolution in Mendelian populations. Genetics, 16:97-159.

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Wright, Sewall 1932. General, Group and Special Size Factors Genetics, 17: 603-619.

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Wright, Sewall 1934. An Analysis of Variability in Number of Digits in an Inbred Strain of Guinea Pigs Genetics, 19: 506-536.

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Wright, Sewall 1934. On the Genetics of Subnormal Development of the Head (otocephaly) in the Guinea Pig Genetics, 19: 471-505.

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Wright, Sewall 1934. The Results of Crosses Between Inbred Strains of Guinea Pigs, Differing in Number of Digits Genetics, 19: 537-551.

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Wright, Sewall 1935. A Mutation of the Guinea Pig, Tending to Restore the Pentadactyl Foot When Heterozygous, Producing a Monstrosity When Homozygous Genetics, 20: 84-107.

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Wright, Sewall and Eaton, O. N. 1926. Mutational Mosaic Coat Patterns of the Guinea Pig Genetics, 11: 333-351.

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Wright, Sewall. 1931. Evolution in Mendelian populations. Genetics, 16:97-159.

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Soon after the establishment of Mendelian genetics, several workers began to explore how Mendelian mechanisms would affect changes in gene frequencies in populations - that is, they began to explore the implications of Mendelism for evolution.

Sewall Wright became one of the leading theoreticians who studied Mendelism in the context of population genetics. This paper is a key presentation of his thinking on how Mendelism and evolution might interact.


Wright, Sewall. 1932. Complementary Factors for Eye Color in Drosophila. The American Naturalist, LXVI:282-283.

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There are two distinct biochemical pathways producing pigments that color the eyes of Drosophila melanogaster -- one yields a bright red pigment, the other brown. When both are present, the eyes are dark-red. When one is present and the other absent, flies have brown or bright red eyes. When both are missing, flies have white eyes.

In 1932, Sewall Wright reported the first case where a cross between red-eyed and brown-eyed flies yielded double-recessive progeny with white eyes. What makes this observation interesting is that the work occurred as part of a class exercise in an undergraduate teaching laboratory at the University of Chicago. Not many modern undergraduate lab exercises yield publishable results.


Yule, G. Udny 1902. Mendel's laws and their probably relations to intra-racial heredity. The New Phytologist, 1:193-207,222-238.

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