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Sturtevant, Alfred Henry

chromosome genes genetics ‘fly

[ ster tevant] (1891–1970) US geneticist: pioneer of chromosome mapping.

As a boy Sturtevant drew up pedigrees for his father’s farm horses, and as a student at Columbia University his older brother encouraged this interest through books on heredity. A book on Mendelism spurred his enthusiasm, since he felt that some horse coat colours could be explained on a Mendelian basis. He wrote on this to the leading American geneticist and in 1910 joined the group of enthusiasts in the crowded ‘fly room’ at Columbia, working with Morgan on the genetics of the fruit fly, Drosophila . In 1928 Sturtevant became professor of genetics at the California Institute of Technology, where he remained, except for research visits, until his death.

In the ‘fly room’ he had the germ of the idea of chromosome mapping and ‘went home, and spent most of the night (to the neglect of my undergraduate homework) in producing the first chromosome map’. This was based on his idea that the frequency of crossing-over between two genes gives an index of their relative distance on a linear map of the genes on the chromosome. His paper of 1913 located six sex-linked genes, as deduced from the way they associated with each other; it forms a classic paper on genetics. He later developed a range of related ideas, discovering the ‘position effect’, ie the way in which the expression of a gene depends on its position in relation to other genes; and he showed that crossing-over between chromosomes is prevented in regions where a part of the chromosome material is inserted the wrong way round. The position effect was to prove of great importance in F Jacob (1920– ) and work on gene clusters (operons) in bacteria. Although Sturtevant’s main work was in genetics (where he worked with a range of animals on an assortment of problems, including the curious effect of direction of shell-coiling in snails) he was also a knowledgeable naturalist, with a special interest in social insects.

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