Thomas Hunt Morgan

(1866—1945) American zoologist

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US geneticist, who confirmed the theory first proposed by Hugo de Vries that exchange of genetic material between homologous (paired) chromosomes takes place during cell division (meiosis) prior to the formation of gametes in living organisms. He received the 1933 Nobel Prize for Physiology or Medicine.

Born in Lexington, Kentucky, Morgan graduated from Kentucky State College with a BS degree in zoology (1886) and obtained his PhD from Johnson Hopkins University four years later. He became a teacher at Bryn Mawr College, Philadelphia, during which time he made several visits to the Naples Zoological Station and began his own work in experimental embryology. In 1904 he was appointed professor of experimental zoology at Columbia University and in 1908 started his series of breeding experiments using the fruit fly Drosophila melanogaster. Morgan and his team, A. H. Sturtevant, C. B. Bridges, and H. J. Muller, found a recessive mutant character, white eye, that was only manifest in male progeny. Morgan proposed that the gene responsible was carried by the sex chromosome, i e it was sex-linked. Previously sceptical, Morgan was convinced by this evidence that chromosomes did carry the genes. Going on to work with two different sex-linked characters, Morgan discovered that they were not always inherited together and so, in 1911, postulated exchange between regions of homologous chromosomes during meiosis – a phenomenon he termed crossing-over. In 1913, A. H. Sturtevant produced the first linkage map, in which he related the frequency of crossing over between any two genes to their notional distance apart on the chromosome. Morgan's team made many further discoveries, all of which firmly established the link between inheritance of characters and chromosomes.

In 1928, Morgan joined the California Institute of Technology to found the biology division. Here he resumed his research in embryology. He served as president of the National Academy of Sciences (1927–31) and wrote The Mechanism of Mendelian Heredity (1915) and The Theory of the Gene (1926).

Subjects: Science and Mathematics.

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