Thomas Hunt Morgan (September 25, 1866 — December 4, 1945) was an American geneticist. He worked on the natural history, zoology, and macromutation in the fruit fly Drosophila. His most important contributions to science were in genetics; he won the Nobel Prize in Physiology or Medicine in 1933 for proving chromosomes to be the carriers of genes. Because of his work, Drosophila became one of the major model organisms in genetics.
Morgan was born in Lexington, Kentucky. Morgan received his bachelor's degree from the University of Kentucky in 1886 and his master's degree in 1888. The Thomas Hunt Morgan School of Biological Sciences at the University of Kentucky is named for Dr. Morgan. He received his Ph.D. from Johns Hopkins University in 1890. Following William E. Castle, he started working on the embryonic development of Drosophila melanogaster (the common fruit fly) at Columbia University, he became interested in heredity. Gregor Mendel's theories had recently been rediscovered around 1900 and Morgan was interested in testing these theories in animals. He began cross-breeding Drosophila, but had no success for two years. Finally in 1910, he noticed a white-eyed mutant male among the red-eyed wild types. He bred this white-eyed fly with a red-eyed female. Their progeny were all red-eyed, suggesting that the white eye trait was recessive. Morgan thus named the gene white, starting the tradition of naming genes after their mutant allele. As Morgan continued to cross-breed the mutants back to one another, he noticed that only males displayed the white-eyed trait. From this, he concluded that (1) some traits were sex-linked, (2) the trait was probably carried on the sex chromosome (ie the X and Y chromosomes), and (3) other genes were probably carried on specific chromosomes as well. He and his students counted the characteristics of thousands of fruit flies and studied their inheritance. Using chromosome recombination, Morgan and Alfred Sturtevant formed a map of genes' locations on the chromosome. Morgan and his students also wrote the seminal book The Mechanism of Mendelian Heredity. Morgan moved to the California Institute of Technology in 1928. Morgan died in Pasadena, California.
Morgan left an important legacy in genetics. Some of Morgan's students from Columbia and Caltech went on to win their own Nobel Prizes, including George Wells Beadle, Edward B. Lewis and Hermann Joseph Muller. In Morgan's honor, the Genetics Society of America annually awards the Thomas Hunt Morgan Medal to one of its members who has made a significant contribution to the science of genetics. Nobel prize winner Eric Kandel has written of Morgan, "Much as Darwin's insights into the evolution of animal species first gave coherence to nineteenth-century biology as a descriptive science, Morgan's findings about genes and their location on chromosomes helped transform biology into an experimental science." The centimorgan, a unit of recombinant frequency used in gene mapping, was named in his honor.