Morgan, Thomas Hunt (1866–1945), American geneticist. Morgan spent much of his career as a professor of experimental biology at Columbia University. He became a pioneer in the developing science of genetics. In 1908 and 1909 he began a series of experiments first with mice and rats and then with fruit flies of the genus Drosophila. During the next several years he discovered many mutant traits, such as eye colors, body colors, and wing variations, and determined the modes of heredity. He and the members of his experimental laboratory made such advances in genetics as a clear understanding of sex-linkage, final proof of the chromosome theory of heredity, establishment of the linear arrangement of genes in the chromosome, the demonstration of interference in crossing-over, and the discovery of chromosomal inversions. He was awarded the Nobel Prize for Physiology or Medicine in 1933.