Thomas Hunt Morgan

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Image:Thomas Hunt Morgan.jpg Thomas Hunt Morgan (September 25, 1866 – December 4, 1945) was an American geneticist and embryologist. Morgan received his B.S. from the State College of Kentucky (University of Kentucky) and later earned his PhD from Johns Hopkins University in 1890, and worked on embryology during his tenure at Bryn Mawr. Following the rediscovery of Mendelian inheritance in 1900, Morgan's research moved to the study of mutation in the fruit fly Drosophila melanogaster. In his famous Fly Room at Columbia University Morgan was able to demonstrate that genes are carried on chromosomes and are the mechanical basis of heredity. These discoveries formed the basis of the modern science of genetics. When he was awarded the Nobel Prize in Physiology or Medicine in 1933 he was the first person awarded the Prize for genetics, for demonstrating hereditary transmission mechanisms in Drosophila melanogaster.

During his distinguished career Morgan wrote 22 books and 370 scientific papers, and as a result of his work Drosophila became a major model organisms in contemporary genetics. The Division of Biology he established at the California Institute of Technology produced seven Nobel Prize winners.

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Early life

Morgan was born in Lexington, Kentucky to Charlton Hunt Morgan and Ellen Key Howard. His family was part of a long line of Southern aristocracy, his father was a nephew of Confederate General John Hunt Morgan and his great-grandfather John Wesley Hunt had been the first millionaire west of the Allegheny Mountains. He was also a great-grandson of Francis Scott Key author of the "Star Spangled Banner". However following the Civil War the family had fallen on harder times with the loss of civil and property rights for those who aided the Confederacy. His father also had difficulty finding work in politics and spent much of his time coordinating veterans reunions.

When Morgan was 16 he attended at the State College of Kentucky (now the University of Kentucky). There, he chose to study science, particularly enjoying natural history, and worked with the federal geological survey in his summers. He graduated as valedictorian in 1886 and was the only student to graduate with a bachelor of science. He chose to undertake graduate studies at Johns Hopkins University, since Hopkins was one of the few universities in the United States at that time which taught biology extensively. After two years of experimental work with William Keith Brooks and several publications Morgan was eligible to receive a master of science from the State College of Kentucky in 1888, the College required two years study at another institution and an examination by the College Faculty. The College offered Morgan a full professorship; however, he choose to stay at Johns Hopkins and was awarded a relatively large fellowship to help him fund his studies.

Morgan completed his experimental work at Woods Hole, Massachusetts at the Marine Biological Laboratory. He studied the embryology of sea spiders to determine their phylogenic relationship with other arthropods. He concluded that with respect to embryology they were more closely related to spiders than crustaceans. Based on the publication of this work Morgan was awarded his Ph.D. from Johns Hopkins in 1890, and was also awarded the Bruce Fellowship in Research. With the Fellowship he was able to travel to Jamaica, the Bahamas and to Europe to conduct further research.

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Bryn Mawr

In 1891, Morgan was appointed the associate professor at Johns Hopkins' sister school Bryn Mawr replacing his colleague Edmund Wilson. He lectured in biology 5 days a week, giving two lectures a day. He frequently included his own recent research in his lectures, and although he was an enthusiastic teacher, his true interests were in the laboratory. During the first few years at Bryn Mawr he produced descriptive studies of sea acorns, ascadian worms and frogs.

In 1894 he was granted a years absence to conduct research in the laboratories of Stazione Zoologica in Naples. At the laboratory in Naples he worked with German biologist Hans Driesch whose research in the experimental study of development piqued Morgan's interest. At the time there was considerable scientific debate over the question of how an embryo formed. One group of scientists believed that the cells were predestined (preformed) to become frogs; the other group thought that development was due to epigenetic factors where interactions between the protoplasam and the nucleus of the egg and the environment could affect development. Morgan was in the later camp, and successfully demonstrated that a daughter cell from a white fish embryo could develop normally into a complete fish confirming Drieschs earlier experiments. He also showed that sea urchin eggs could be induced to divide without fertilization by adding magnesium chloride, work which was continued by Jacques Loeb who became well known for creating fatherless frogs using the method.

Morgan returned to Bryn Mawr in 1895 and was promoted to full professor. He wrote his first book The Development of the Frog's Egg and it was published in 1897. He began a series of studies on different organisms ability to regenerate. He looked at grafting and regeneration in tadpoles, fish and earthworms and in 1901 this work was published as Regeneration.

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Columbia University

In 1903, Morgan was offered the United States first professorship in experimental zoology at Columbia University by Edmund Beecher Wilson. In the same year he became engaged and married former student Lilian Vaughan Sampson. The couple moved to New York and had four children. Morgan was soon engaged in research in the newly rediscovered field of genetics.

In 1900 three scientists, Carl Correns, Erich von Tschermak and Hugo De Vries had rediscovered the work of Gregor Mendel. De Vries had gone on to propose that new species are created by mutation. Morgan was quite skeptical of Gregor Mendel's laws of heredity, which had been recently stirred up with the emerging Darwinian and Lamarckian theories of evolution. Morgan dismissed both of these evolutionary theories, and was actually seeking to prove Hugo De Vries' mutation theory with his Drosophila experiments.

Image:Sexlinked inheritance white.jpg Following C. W. Woodworth and William E. Castle, Morgan started working on the Drosophila melanogaster. Working with Fernandus Payne he mutated Drosophila with X-rays and began cross-breeding experiments, but had no visible success for two years. Castle had also had difficulty identifying mutations in Drosophila, hardly unusual given the flies' tiny size. Finally in 1910, Morgan 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. Morgan also discovered a pink-eyed mutant that showed a different pattern of inheritance. He wrote a paper which was published in Science in 1911, he concluded that (1) some traits were sex-linked, (2) the trait was probably carried on one of the sex chromosomes, and (3) other genes were probably carried on specific chromosomes as well.

Morgan and his students became more successful at finding mutant flies and counted the mutant characteristics of thousands of fruit flies and studied their inheritance. The observation of a miniature wing mutant which was also on the sex chromosome but sometimes sorted independently to the white eye mutation, led Morgan to the idea of genetic linkage. Morgan proposed that the amount of crossing over between linked genes differs and that crossover frequency might indicate the distance separating genes on the chromosome, later English geneticist J. B. S. Haldane suggested that the unit of measurement be called the morgan. Morgan's student Alfred Sturtevant developed the first genetic map in 1913.

In 1915 Morgan, Sturtevant, Calvin Bridges and H. J. Muller wrote the seminal book The Mechanism of Mendelian Inheritance. Geneticist Curt Stern called the book "the fundamental textbook of the new genetics" and C. H. Waddington noted that "Morgan's theory of the chromosome represents a great leap of imagination comparable with Galileo or Newton". Following the book's publication, Morgan was established as the twentieth century's Mendel. John Hopkins awarded Morgan an honorary LL.D. and the University of Kentucky awarded him an honorary Ph.D. He was elected a member of the National Academy of Sciences and made a foreign member of the Royal Society. In 1924 Morgan received the Darwin Medal. His Fly Room at Columbia became world famous and he found it easy to attract funding and visiting academics. In 1927 after 25 years at Columbia, and nearing the age of retirement he received an offer from George Ellery Hale to establish a school of biology in California.

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Caltech

Morgan moved to California to head the Division of Biology at the California Institute of Technology in 1928. In establishing the biology division, Morgan wanted to distinguish his program from those offered by Johns Hopkins and Columbia, with research focussed on genetics and evolution; experimental embryology; physiology; biophysics and biochemistry. He was also instrumental in the establishment of the Marine Laboratory on Corona del Mar. He wanted to attract the best people to the Division at Caltech, so he took Bridges, Sturtevant, Jack Shultz and Albert Tyler from Columbia and took on Theodosius Dobzhansky as an international research fellow. More scientists came to work in the Division including George Beadle, Boris Ephrussi, Edward L. Tatum, Linus Pauling, Frits Went, and Sidney W. Fox.

In accordance with his reputation, Morgan held numerous prestigious positions in American science organizations. From 1927 to 1931 Morgan served as the President of the National Academy of Sciences; in 1930 he was the President of the American Association for the Advancement of Science; and in 1932 he chaired the Sixth International Congress of Genetics in Ithaca, New York. In 1933 Morgan was awarded the Nobel Prize in Physiology or Medicine; he has been nominated in 1919 and 1930 for the same work. As an acknowledgement of the group nature of his discovery he gave his prize money to Bridges', Sturtevant's and his own children. Morgan declined to attend the awards ceremony in 1933, instead attending in 1934. The 1933 rediscovery of the giant polytene chromosomes in the salivary glad of Drosophila may have influenced his choice. Until that point, the lab's results had been inferred from phenotypic results, the visible polytene chromosome enabled them to confirm their results on a physical basis. Morgan's Nobel acceptance speech entitled "The Contribution of Genetics to Physiology and Medicine" downplayed the contribution genetics could make to medicine beyond genetic counselling. In 1939 he was awarded the Copley Medal by the Royal Society.

He received two extensions of his contract at Caltech, but eventually retired in 1942, becoming professor and chairman emeritus. George Beadle returned to Caltech to replace Morgan as chairman of the department in 1946. Although he had retired, Morgan kept offices across the road from the Division and continued laboratory work. In his retirement he returned to the questions of sexual differentiation, regeneration, and embryology. Morgan had throughout his life suffered with a chronic duodenal ulcer, and in 1945 he experienced a severe attack and died from a ruptured artery.

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Legacy

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. 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 Thomas Hunt Morgan School of Biological Sciences at the University of Kentucky is named for Morgan. 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.

Thomas Hunt Morgan's discovery was illustrated on a 1989 stamp issued in Sweden, showing the discoveries of eight Nobel Prize winning geneticists.

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References

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External links

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