Morgan, Thomas Hunt (1866–1945)

US geneticist who was awarded the Nobel Prize for Physiology or Medicine in 1933 for his work on the role of chromosomes in heredity. He helped establish that genes are located on the chromosomes, discovered sex chromosomes, and invented the techniques of genetic mapping. He was the first to work on the fruit fly Drosophila, which has since become a major subject of genetic studies.

Morgan was born in Lexington, Kentucky, and studied at Johns Hopkins University. He was professor of experimental zoology at Columbia University in the period 1904–28, when he was appointed director of the Laboratory of Biological Sciences at the California Institute of Technology.

Following the rediscovery of Austrian scientist Gregor Mendel's work, Morgan's interest turned from embryology to the mechanisms involved in heredity, and in 1908 he began his research on the genetics of Drosophila. From his findings he postulated that certain characteristics are sex-linked, that the X-chromosome carries several discrete hereditary units (genes), and that the genes are linearly arranged on chromosomes. He also demonstrated that sex-linked characters are not invariably inherited together, from which he developed the concept of crossing-over and the associated idea that the extent of crossing-over is a measure of the spatial separation of genes on chromosomes.

Morgan published a summary of his work in The Mechanism of Mendelian Heredity (1915).