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Tuesday, October 2, 2012

Thomas Hunt Morgan

 


The American zoologist and geneticist Thomas Hunt Morgan (1866-1945) established the theory of the gene which helped clarify the process of evolution and formed the modern basis of heredity.
Thomas Hunt Morgan, born on Sept. 25, 1866, in Lexington, Ky., was the son of Charlton and Ellen Morgan. He was descended on both sides from English Cavalier stock. In 1886 he entered the State College of Kentucky and later studied at Johns Hopkins University, where he divided his time between morphology and physiology. In 1890 he received his doctorate for a paper on the embryology and phylogeny of sea spiders. In 1891 he served as professor of biology at Bryn Mawr College, after which he went to Europe for further study, first in Germany and then at the famous zoological station at Naples, Italy. There he met Hans Driesch, the philosopher-scientist who believed in "vitalism." Morgan, however, favored a mechanistic approach to the solution of biological problems.
Upon his return to the United States in 1904, Morgan accepted a professorship at Columbia University which lasted until 1928. While there he undertook a series of breeding experiments to assess the reality of genes as the particles of heredity. Morgan chose the fruit fly (Drosophila melanogaster) for his experiments because it was a short-lived organism that could easily be bred in the laboratory under changing condition and could complete its life cycle in about 10 days, supplying as many as 30 generations a year.
Morgan's experiments were so successful that by 1914 he had proved the chromosome theory of heredity as a result of breeding and cytological examination. In 1910 he found his first mutant and proceeded to cross this fly with a normal one. The percentages of normal and mutant offspring were in accordance with Mendel's law of inheritance. Morgan found many mutant characters and soon discovered that certain characteristics not only were sex-linked but also tended to appear together in certain flies. From this he postulated that all sex-linked characters tended to be inherited together because they were associated as a unit on a single chromosome in the nucleus of the original cell. Morgan called these characters linkage groups. By the summer of 1914 three linkage groups had been discovered. He used the word "gene" to represent each character unit, and the exact positions of these genes in the chromosomes was worked out by Alfred Henry Sturtevant, one of Morgan's former students and a member of his research staff. In 1915 Morgan and his assistants published The Mechanism of Mendelian Heredity to describe the system of genes. Later he published The Theory of the Gene (1926), his culminating work on the subject which discussed at length the chromosome theory of heredity.
In 1928 Morgan established the Kerckhoff Laboratories of Biological Sciences at the California Institute of Technology in Pasadena, which became the leading center for research genetics. In 1933 he received the Nobel Prize in physiology or medicine in recognition of the significance of his theory of heredity for physiology and for the part that the new genetics was destined to play in the future of medicine.
In 1941 Morgan retired as active head of his department at Cal Tech. However, he continued to work on problems in embryology which he had first approached in 1903--trying to find out why the spermatozoon of the common hermaphroditic sea squirt almost never fertilizes the egg of the same individual (self-sterilization) but does fertilize eggs of all other sea squirts. On Dec. 4, 1945, the grand old man of genetics passed away.

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