The white-eyed fly: a gene tied to a chromosome, linkage and the first genetic map

1910–1915 Life and health observation

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The discovery that a gene is attached to a chromosome and that characters lying on the same chromosome are inherited together, though not absolutely; the frequency of broken linkage serves as a measure of the distance between genes and allows a linear genetic map to be built.

The discovery was made in 1910 by the American Thomas Hunt Morgan, who took up the fruit fly Drosophila without believing either in Mendelism or in the chromosome hypothesis, he wanted to test de Vries's mutation theory on animals. In January 1910 a male with white eyes appeared in one of the bottles; in crosses white eyes behaved as a Mendelian recessive character but went almost always to males. The only explanation was that the eye-colour factor sat on the same chromosome that determines sex. Other sex-linked mutations then accumulated, and they were not completely linked: the American Alfred Sturtevant, still an undergraduate, in 1913 turned the frequency of broken linkage into distance and built a linear map of six genes on the X chromosome.

The 1915 book gathered this into a mechanism: genes lie on chromosomes in linear order, and Mendel's laws describe observable events in the cell.

Why this date

The date follows 1910, the year of the paper 'Sex limited inheritance in Drosophila', Science 32, pp. 120-122 (July 1910); the white-eyed male was found in January 1910, and the circumstances of the find are, according to Green, disputed, Morgan later asserting that he found the fly himself. The upper bound of the label is the book by Morgan, Sturtevant, Muller and Bridges, 'The Mechanism of Mendelian Heredity' (New York: Holt, 1915). The map of six sex-linked factors: A. H. Sturtevant, Journal of Experimental Zoology 14 (1913), pp. 43-59. Wikidata points to the 1910 paper (Q55044447); the 1915 book has its own entry, Q42192791, not used here.

What it grew from

• Three papers of 1900: de Vries, Correns and Tschermak bring back Mendel's laws

  influenced · Confidence: high

  Morgan took up Drosophila not as a Mendelian but as a sceptic: he was irritated by the way facts were being turned into 'factors' after 1900, and he kept flies in order to test Mendelism and the mutation theory with his own hands.

  Dispute: Allen gives a different nearest motive: to test de Vries's mutation theory on animals. The two versions are compatible, since de Vries is himself one of the rediscoverers, but the influence here means a challenge rather than a descent.

  Link sources

  • M. M. Green, 2010: A Century of Drosophila Genetics Through the Prism of the white Gene, Genetics 184 (1), 3-7 (2010) Verified 20 Sep 2026

    As Sturtevant (2001), in a reminiscence of Morgan given in 1967, confirms, “this didn't suit Morgan. So by about 1910, he could fairly be described as anti-Mendelian.” Morgan's skepticism moved him to see for himself the plausibility of Mendelism by searching for heritable phenotypic changes in the vinegar fly, Drosophila melanogaster.

  • Garland E. Allen, Morgan, Thomas Hunt, Complete Dictionary of Scientific Biography (1974) Verified 20 Sep 2026

    Morgan’s original purpose had been to test de Vries’s mutation theory in animals.

  • M. M. Green, 2010: A Century of Drosophila Genetics Through the Prism of the white Gene, Genetics 184 (1), 3-7 (2010) Verified 20 Sep 2026

    “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.”

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

• 'The Chromosomes in Heredity': chromosome behaviour as the physical basis of Mendel's laws

  influenced · Confidence: high

  The white-eyed fly gave the first concrete evidence for what Sutton had proposed as a hypothesis: the inheritance of a character followed the segregation of a particular chromosome. Morgan began as an opponent of the chromosome hypothesis and accepted it when he arrived at it by an independent route.

  Dispute: The link is not direct discipleship: Martins shows that Morgan rejected Sutton's hypothesis and that the rejection was well founded given the state of cytology at the time. Allen writes that what convinced Morgan was the work of Wilson and Stevens on sex chromosomes and his own experiments, not a reading of Sutton. Green speaks of a continuity of result, not of intention.

  Link sources

  • M. M. Green, 2010: A Century of Drosophila Genetics Through the Prism of the white Gene, Genetics 184 (1), 3-7 (2010) Verified 20 Sep 2026

    The result of breeding the white male to red females and additional crosses in subsequent generations led Morgan to the conclusion that the inheritance of white eye color parallels the normal meiotic segregation of the sex chromosomes in this fly. This represented the first concrete evidence that chromosomes have a role in inheritance as had been suggested nearly a decade earlier by Sutton and Boveri.

  • Garland E. Allen, Morgan, Thomas Hunt, Complete Dictionary of Scientific Biography (1974) Verified 20 Sep 2026

    Much to his credit, he rejected his skepticism about both the Mendelian and the chromosome theories when he saw from two independent lines of evidence (breeding experiments and cytology) that one could be treated in terms of the other.

  • Lilian Al-Chueyr Pereira Martins, Did Sutton and Boveri propose the so-called Sutton-Boveri chromosome hypothesis?, Genetics and Molecular Biology 22 (2), 261-272 (1999) Verified 20 Sep 2026

    For those reasons, the attitudes of those scholars who denied it, such as Thomas Hunt Morgan (Martins, 1998) or those who adopted an attitude of critical expectation, such as William Bateson (Martins, 1997 a,b) can be regarded as scientifically sound.

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

• Boveri's multipolar mitoses: chromosomes are qualitatively different and individual

  influenced · Confidence: medium

  Boveri's argument that chromosomes differ in quality and that each is needed for development made it sensible to ask what exactly sits on a particular chromosome; it was this question that Morgan's white-eyed fly answered.

  Dispute: Green names Sutton and Boveri together, while Martins holds that joining the names is unfair and shows that Boveri published no chromosome hypothesis of heredity in 1902-1903. The Boveri to Morgan link is therefore weaker than Sutton to Morgan: in Oppenheimer it is a retrospective assessment, not a claim of direct influence.

  Link sources

  • M. M. Green, 2010: A Century of Drosophila Genetics Through the Prism of the white Gene, Genetics 184 (1), 3-7 (2010) Verified 20 Sep 2026

    This represented the first concrete evidence that chromosomes have a role in inheritance as had been suggested nearly a decade earlier by Sutton and Boveri.

  • Jane Oppenheimer, Boveri, Theodor, Complete Dictionary of Scientific Biography (1970) Verified 20 Sep 2026

    When these words appeared in print, Thomas Hunt Morgan’s the ory of the Gene had not yet been published, and evidence for the linear order of genes had not yet been presented. Fifty years later, when the chromosomal basis of heredity had not only been firmly established but had also been successfully elucidated at a molecular level, the fruitfulness of Boveri’s discoveries and conceptions became fully apparent.

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

Links under review

• Johannsen: pure lines, genotype and phenotype

  influenced · Confidence: low

  A link between concepts, not a documented influence: the source (Greene) speaks of the genotype-phenotype distinction, not of Johannsen's effect on Morgan.

  Morgan received the word 'gene' ready-made from Johannsen, and the Drosophila work filled it with material content: the abstract Mendelian 'factor' became something lying at a definite place on a definite chromosome.

  Dispute: The quotation asserts a connection of concepts, not an effect of Johannsen upon Morgan: there is no mention of reading or correspondence, and Johannsen himself insisted that the genotype is not reducible to material particles.

  Link sources

  • M. M. Green, 2010: A Century of Drosophila Genetics Through the Prism of the white Gene, Genetics 184 (1), 3-7 (2010) Verified 20 Sep 2026

    So began a short 1910 Science article by T. H. Morgan on the inheritance of the white eye phenotype. Thus began the transformation of Mendel's rather abstract hereditary “factors” to Johanssen's more concrete, if still mysterious, “genes.”

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

Node sources

• Garland E. Allen, Morgan, Thomas Hunt, Complete Dictionary of Scientific Biography (1974) Verified 20 Sep 2026

  In 1910 Morgan discovered a small, distinct variation in one male fly in one of his culture bottles. This fly had white, as opposed to the normal (wildtype) red, eye color.

• Garland E. Allen, Morgan, Thomas Hunt, Complete Dictionary of Scientific Biography (1974) Verified 20 Sep 2026

  Morgan found that the only way he could explain this phenomenon was to assume that the red-and white-eye conditions were determined by Mendelian factors, and that these somehow associated with the element which determined sex in the cell.

• Garland E. Allen, Morgan, Thomas Hunt, Complete Dictionary of Scientific Biography (1974) Verified 20 Sep 2026

  During a conversation with Morgan in 1911, Sturtevant, then still an undergraduate, suddenly realized that the variations in strength of linkage could be used as a means of determining the relative spatial distances of genes on a chromosome.

• Garland E. Allen, Morgan, Thomas Hunt, Complete Dictionary of Scientific Biography (1974) Verified 20 Sep 2026

  The major early findings of the Drosophila group were summarized in an epoch-making book, The Mechanism of Mendelian Heredity, published by Morgan, Bridges, Sturtevant, and Muller in 1915. They presented evidence to suggest that genes were linearly arranged on chromosomes and that it was possible to regard the Mendelian laws as based on observable events taking place in cells.

• M. M. Green, 2010: A Century of Drosophila Genetics Through the Prism of the white Gene, Genetics 184 (1), 3-7 (2010) Verified 20 Sep 2026

  Interestingly, neither the discoverer nor the exact date of discovery of the white-eyed fly are stated in Morgan's article. Unsurprisingly, as a result of those omissions, the exact “who” and “when” became controversial.

• M. M. Green, 2010: A Century of Drosophila Genetics Through the Prism of the white Gene, Genetics 184 (1), 3-7 (2010) Verified 20 Sep 2026

  Using recombination frequency as a measure of genetic distance, A. H. Sturtevant (1913) as an undergraduate student, (later Morgan's graduate student), in a tour de force constructed a linear genetic map of the six sex-linked mutations.

• M. M. Green, 2010: A Century of Drosophila Genetics Through the Prism of the white Gene, Genetics 184 (1), 3-7 (2010) Verified 20 Sep 2026

  Morgan, T. H., 1910. Sex-limited inheritance in Drosophila. Science 32 120–122.

"Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

Open this node on the map · Wikidata: Q55044447