Thomas Hunt Morgan

Thomas Hunt Morgan (September 25, 1866 – December 4, 1945)[2] was an American evolutionary biologist, geneticist, embryologist, and science author who won the Nobel Prize in Physiology or Medicine in 1933 for discoveries elucidating the role that the chromosome plays in heredity.[3]

Morgan received his Ph.D. from Johns Hopkins University in zoology in 1890 and researched embryology during his tenure at Bryn Mawr. Following the rediscovery of Mendelian inheritance in 1900, Morgan began to study the genetic characteristics of the fruit fly Drosophila melanogaster. In his famous Fly Room at Columbia University, Morgan demonstrated that genes are carried on chromosomes and are the mechanical basis of heredity. These discoveries formed the basis of the modern science of genetics.

During his distinguished career, Morgan wrote 22 books and 370 scientific papers.[2] As a result of his work, Drosophila became a major model organism in contemporary genetics. The Division of Biology which he established at the California Institute of Technology has produced seven Nobel Prize winners.

Thomas Hunt Morgan

Thomas Hunt Morgan
Johns Hopkins yearbook of 1891
BornSeptember 25, 1866
DiedDecember 4, 1945 (aged 79)
NationalityUnited States
Alma mater
Known for
Awards
Scientific career
Fields
Institutions
Doctoral students
Signature
Thomas Hunt Morgan signature

Early life and education

Morgan was born in Lexington, Kentucky, to Charlton Hunt Morgan and Ellen Key Howard Morgan.[3][4] Part of a line of Southern planter elite on his father's side, Morgan was a nephew of Confederate General John Hunt Morgan; his great-grandfather John Wesley Hunt had been the first millionaire west of the Allegheny Mountains. Through his mother, he was the great-grandson of Francis Scott Key, the author of the "Star Spangled Banner", and John Eager Howard, governor and senator from Maryland.[4] Following the Civil War, the family fell on hard times with the temporary loss of civil and some property rights for those who aided the Confederacy. His father had difficulty finding work in politics and spent much of his time coordinating veterans reunions.

Beginning at age 16 in the Preparatory Department, Morgan attended the State College of Kentucky (now the University of Kentucky). He focused on science; he particularly enjoyed natural history, and worked with the U.S. Geological Survey in his summers. He graduated as valedictorian in 1886 with a Bachelor of Science degree.[5] Following a summer at the Marine Biology School in Annisquam, Massachusetts, Morgan began graduate studies in zoology at the recently founded Johns Hopkins University, the first research-oriented American university. After two years of experimental work with morphologist William Keith Brooks and writing several publications, Morgan was eligible to receive a master of science from the State College of Kentucky in 1888. The college required two years of study at another institution and an examination by the college faculty. The college offered Morgan a full professorship; however, he chose to stay at Johns Hopkins and was awarded a relatively large fellowship to help him fund his studies.

Under Brooks, Morgan completed his thesis work on the embryology of sea spiders—collected during the summers of 1889 and 1890 at the Marine Biological Laboratory in Woods Hole, Massachusetts—to determine their phylogenetic 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. He used the fellowship to travel to Jamaica, the Bahamas and to Europe to conduct further research.[6]

Nearly every summer from 1890 to 1942, Morgan returned to the Marine Biological Laboratory to conduct research. He became very involved in governance of the institution, including serving as an MBL trustee from 1897 to 1945.[7]

Career and research

Morgan's career and research can be broken into several phases:

Bryn Mawr

In 1890, Morgan was appointed associate professor (and head of the biology department) at Johns Hopkins' sister school Bryn Mawr College, replacing his colleague Edmund Beecher Wilson.[8] Morgan taught all morphology-related courses, while the other member of the department, Jacques Loeb, taught the physiological courses. Although Loeb stayed for only one year, it was the beginning of their lifelong friendship.[9] Morgan lectured in biology five days a week, giving two lectures a day. He frequently included his own recent research in his lectures. Although an enthusiastic teacher, he was most interested in research in the laboratory. During the first few years at Bryn Mawr, he produced descriptive studies of sea acorns, ascidian worms and frogs.

In 1894 Morgan was granted a year's absence to conduct research in the laboratories of Stazione Zoologica in Naples, where Wilson had worked two years earlier. There he worked with German biologist Hans Driesch, whose research in the experimental study of development piqued Morgan's interest. Among other projects that year, Morgan completed an experimental study of ctenophore embryology. In Naples and through Loeb, he became familiar with the Entwicklungsmechanik (roughly, "developmental mechanics") school of experimental biology. It was a reaction to the vitalistic Naturphilosophie, which was extremely influential in 19th-century morphology. Morgan changed his work from traditional, largely descriptive morphology to an experimental embryology that sought physical and chemical explanations for organismal development.[10]

At the time, there was considerable scientific debate over the question of how an embryo developed. Following Wilhelm Roux's mosaic theory of development, some believed that hereditary material was divided among embryonic cells, which were predestined to form particular parts of a mature organism. Driesch and others thought that development was due to epigenetic factors, where interactions between the protoplasm and the nucleus of the egg and the environment could affect development. Morgan was in the latter camp; his work with Driesch demonstrated that blastomeres isolated from sea urchin and ctenophore eggs could develop into complete larvae, contrary to the predictions (and experimental evidence) of Roux's supporters.[11] A related debate involved the role of epigenetic and environmental factors in development; on this front Morgan showed that sea urchin eggs could be induced to divide without fertilization by adding magnesium chloride. Loeb continued this work and became well known for creating fatherless frogs using the method.[12] [13]

When Morgan returned to Bryn Mawr in 1895, he was promoted to full professor. Morgan's main lines of experimental work involved regeneration and larval development; in each case, his goal was to distinguish internal and external causes to shed light on the Roux-Driesch debate. He wrote his first book, The Development of the Frog's Egg (1897). He began a series of studies on different organisms' ability to regenerate. He looked at grafting and regeneration in tadpoles, fish and earthworms; in 1901 he published his research as Regeneration.

Beginning in 1900, Morgan started working on the problem of sex determination, which he had previously dismissed when Nettie Stevens discovered the impact of the Y chromosome on sex. He also continued to study the evolutionary problems that had been the focus of his earliest work.[14]

Columbia University

Later in 1904, E. B. Wilson—still blazing the path for his younger friend—invited Morgan to join him at Columbia University. This move freed him to focus fully on experimental work.[15]

Drosophila in the lab
In a typical Drosophila genetics experiment, male and female flies with known phenotypes are put in a jar to mate; females must be virgins. Eggs are laid in porridge which the larva feed on; when the life cycle is complete, the progeny are scored for inheritance of the trait of interest.

When Morgan took the professorship in experimental zoology, he became increasingly focused on the mechanisms of heredity and evolution. He had published Evolution and Adaptation (1903); like many biologists at the time, he saw evidence for biological evolution (as in the common descent of similar species) but rejected Darwin's proposed mechanism of natural selection acting on small, constantly produced variations.

Extensive work in biometry seemed to indicate that continuous natural variation had distinct limits and did not represent heritable changes. Embryological development posed an additional problem in Morgan's view, as selection could not act on the early, incomplete stages of highly complex organs such as the eye. The common solution of the Lamarckian mechanism of inheritance of acquired characters, which featured prominently in Darwin's theory, was increasingly rejected by biologists. According to Morgan's biographer Garland Allen, he was also hindered by his views on taxonomy: he thought that species were entirely artificial creations that distorted the continuously variable range of real forms, while he held a "typological" view of larger taxa and could see no way that one such group could transform into another. But while Morgan was skeptical of natural selection for many years, his theories of heredity and variation were radically transformed through his conversion to Mendelism.[16]

In 1900 three scientists, Carl Correns, Erich von Tschermak and Hugo De Vries, had rediscovered the work of Gregor Mendel, and with it the foundation of genetics. De Vries proposed that new species were created by mutation, bypassing the need for either Lamarckism or Darwinism. As Morgan had dismissed both evolutionary theories, he was seeking to prove De Vries' mutation theory with his experimental heredity work. He was initially skeptical of Mendel's laws of heredity (as well as the related chromosomal theory of sex determination), which were being considered as a possible basis for natural selection.

Sexlinked inheritance white
Sex linked inheritance of the white eyed mutation.

Following C. W. Woodworth and William E. Castle, around 1908 Morgan started working on the fruit fly Drosophila melanogaster, and encouraging students to do so as well. With Fernandus Payne, he mutated Drosophila through physical, chemical, and radiational means.[17][18] He began cross-breeding experiments to find heritable mutations, but they had no significant success for two years.[17] Castle had also had difficulty identifying mutations in Drosophila, which were tiny. Finally in 1909, a series of heritable mutants appeared, some of which displayed Mendelian inheritance patterns; in 1910 Morgan noticed a white-eyed mutant male among the red-eyed wild types. When white-eyed flies were bred with a red-eyed female, their progeny were all red-eyed. A second generation cross produced white-eyed males—a sex-linked recessive trait, the gene for which Morgan named white. Morgan also discovered a pink-eyed mutant that showed a different pattern of inheritance. In a paper 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 crossover 1
Morgan's illustration of crossing over, from his 1916 A Critique of the Theory of Evolution

Morgan and his students became more successful at finding mutant flies; they counted the mutant characteristics of thousands of fruit flies and studied their inheritance. As they accumulated multiple mutants, they combined them to study more complex inheritance patterns. 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 and to hypothesize the phenomenon of crossing over. He relied on the discovery of Frans Alfons Janssens, a Belgian professor at the University of Leuven, who described the phenomenon in 1909 and had called it chiasmatypie. 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. The later English geneticist J. B. S. Haldane suggested that the unit of measurement for linkage be called the morgan. Morgan's student Alfred Sturtevant developed the first genetic map in 1913.

Drosophila Gene Linkage Map
Thomas Hunt Morgan's Drosophila melanogaster genetic linkage map. This was the first successful gene mapping work and provides important evidence for the chromosome theory of inheritance. The map shows the relative positions of allelic characteristics on the second Drosophila chromosome. The distance between the genes (map units) are equal to the percentage of crossing-over events that occurs between different alleles. [19]

In 1915 Morgan, Sturtevant, Calvin Bridges and H. J. Muller wrote the seminal book The Mechanism of Mendelian Heredity.[20] 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".

In the following years, most biologists came to accept the Mendelian-chromosome theory, which was independently proposed by Walter Sutton and Theodor Boveri in 1902/1903, and elaborated and expanded by Morgan and his students. Garland Allen characterized the post-1915 period as one of normal science, in which "The activities of 'geneticists' were aimed at further elucidation of the details and implications of the Mendelian-chromosome theory developed between 1910 and 1915." But, the details of the increasingly complex theory, as well as the concept of the gene and its physical nature, were still controversial. Critics such as W. E. Castle pointed to contrary results in other organisms, suggesting that genes interact with each other, while Richard Goldschmidt and others thought there was no compelling reason to view genes as discrete units residing on chromosomes.[21]

Because of Morgan's dramatic success with Drosophila, many other labs throughout the world took up fruit fly genetics. Columbia became the center of an informal exchange network, through which promising mutant Drosophila strains were transferred from lab to lab; Drosophila became one of the first, and for some time the most widely used, model organisms.[22] Morgan's group remained highly productive, but Morgan largely withdrew from doing fly work and gave his lab members considerable freedom in designing and carrying out their own experiments.

He returned to embryology and worked to encourage the spread of genetics research to other organisms and the spread of the mechanistic experimental approach (Enwicklungsmechanik) to all biological fields.[23] After 1915, he also became a strong critic of the growing eugenics movement. This adopted the ideas of genetics in support of racism and worse.[24]

Morgan's 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.

Caltech

Thomas Hunt Morgan sketch 1931
1931 drawing of Thomas Hunt Morgan

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 focused on genetics and evolution; experimental embryology; physiology; biophysics and biochemistry. He was also instrumental in the establishment of the Marine Laboratory at 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 had 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 gland 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. In 1945, at age 79, he experienced a severe heart attack and died from a ruptured artery.

Morgan and evolution

Morgan was interested in evolution throughout his life. He wrote his thesis on the phylogeny of sea spiders (pycnogonids) and wrote four books about evolution. In Evolution and Adaptation (1903), he argued the anti-Darwinist position that selection could never produce wholly new species by acting on slight individual differences.[25] He rejected Darwin's theory of sexual selection[26] and the Neo-Lamarckian theory of the inheritance of acquired characters.[27] Morgan was not the only scientist attacking natural selection. The period 1875–1925 has been called 'The eclipse of Darwinism'.[28] After discovering many small stable heritable mutations in Drosophila, Morgan gradually changed his mind. The relevance of mutations for evolution is that only characters that are inherited can have an effect in evolution. Since Morgan (1915) 'solved the problem of heredity', he was in a unique position to examine critically Darwin's theory of natural selection.

In A Critique of the Theory of Evolution (1916), Morgan discussed questions such as: "Does selection play any role in evolution? How can selection produce anything new? Is selection no more than the elimination of the unfit? Is selection a creative force?" After eliminating some misunderstandings and explaining in detail the new science of Mendelian heredity and its chromosomal basis, Morgan concludes, "the evidence shows clearly that the characters of wild animals and plants, as well as those of domesticated races, are inherited both in the wild and in domesticated forms according to the Mendel's Law". "Evolution has taken place by the incorporation into the race of those mutations that are beneficial to the life and reproduction of the organism".[29] Injurious mutations have practically no chance of becoming established.[30] Far from rejecting evolution, as the title of his 1916 book may suggest, Morgan laid the foundation of the science of genetics. He also laid the theoretical foundation for the mechanism of evolution: natural selection. Heredity was a central plank of Darwin's theory of natural selection, but Darwin could not provide a working theory of heredity. Darwinism could not progress without a correct theory of genetics. By creating that foundation, Morgan contributed to the neo-Darwinian synthesis, despite his criticism of Darwin at the beginning of his career. Much work on the Evolutionary Synthesis remained to be done.

Awards and honors

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 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."[31]

  • Johns Hopkins awarded Morgan an honorary LL.D. and the University of Kentucky awarded him an honorary Ph.D.
  • He was elected Member of the National Academy of Sciences in 1909.[1]
  • He was elected a Foreign Member of the Royal Society (ForMemRS) in 1919[2]
  • In 1924 Morgan received the Darwin Medal.
  • The Thomas Hunt Morgan School of Biological Sciences at the University of Kentucky is named for him.
  • The Genetics Society of America annually awards the Thomas Hunt Morgan Medal, named in his honor, 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.
  • A junior high school in Shoreline, Washington was named in Morgan's honor for the latter half of the 20th century.

Personal life

On June 4, 1904, Morgan married Lillian Vaughan Sampson (1870–1952), who had entered graduate school in biology at Bryn Mawr the same year Morgan joined the faculty; she put aside her scientific work in the early years of their marriage, when they had four children. Later she contributed significantly to Morgan's Drosophila work. One of their four children (one boy and three girls) was Isabel Morgan (1911–1996) (marr. Mountain), who became a virologist at Johns Hopkins, specializing in polio research.

Morgan was an atheist.[32][33][34][35]

References

  1. ^ a b "Thomas Morgan". Nasonline.org. Retrieved 28 April 2019.
  2. ^ a b c d Fisher, R. A.; De Beer, G. R. (1947). "Thomas Hunt Morgan. 1866-1945". Obituary Notices of Fellows of the Royal Society. 5 (15): 451–466. doi:10.1098/rsbm.1947.0011. JSTOR 769094.
  3. ^ a b "The Nobel Prize in Physiology or Medicine 1933". Nobel Web AB. Retrieved 2010-09-14.
  4. ^ a b Sturtevant (1959), p283.
  5. ^ Allen (1978), pp11-14, 24.
  6. ^ Allen, Thomas Hunt Morgan: The Man and His Science, pp 46-51
  7. ^ Kenney, D. E.; Borisy, G. G. (2009). "Thomas Hunt Morgan at the Marine Biological Laboratory: Naturalist and Experimentalist". Genetics. 181 (3): 841–846. doi:10.1534/genetics.109.101659. PMC 2651058.
  8. ^ Morgan, T. H. (1940). "Edmund Beecher Wilson. 1856-1939". Obituary Notices of Fellows of the Royal Society. 3 (8): 123–126. doi:10.1098/rsbm.1940.0012.
  9. ^ Allen, Thomas Hunt Morgan, pp 50-53
  10. ^ Allen, Thomas Hunt Morgan, pp 55-59, 72-80
  11. ^ Allen, Thomas Hunt Morgan, pp 55-59, 80-82
  12. ^ Loeb, Jacques (1899). "On the Nature of the Process of Fertilization and the Artificial Production of Normal Larvae (Plutei) from the Unfertilized Eggs of the Sea Urchin". American Journal of Physiology. 31: 135–138.
  13. ^ Loeb, Jacques (1913). Artificial parthenogenesis and fertilization. University of Chicago Press.
  14. ^ Allen, Thomas Hunt Morgan, pp 84-96
  15. ^ Allen, Thomas Hunt Morgan, pp 68-70
  16. ^ Allen, Thomas Hunt Morgan: The Man and His Science, pp 105-116
  17. ^ a b Kohler, Lords of the Fly, pp 37-43
  18. ^ Hamilton, Vivien (2016). "The Secrets of Life: Historian Luis Campos resurrects radium's role in early genetics research". Distillations. 2 (2): 44–45. Retrieved 22 March 2018.
  19. ^ Mader, Sylvia (2007). Biology Ninth Edition. New York: McGraw-Hill. p. 209. ISBN 978-0-07-325839-3.
  20. ^ Morgan, Thomas Hunt; Alfred H. Sturtevant, H. J. Muller and C. B. Bridges (1915). The Mechanism of Mendelian Heredity. New York: Henry Holt.CS1 maint: Multiple names: authors list (link)
  21. ^ Allen, Thomas Hunt Morgan, pp 208-213, 257-278. Quotation from p 213.
  22. ^ Kohler, Lords of the Fly, chapter 5
  23. ^ Allen, Thomas Hunt Morgan, pp 214-215, 285
  24. ^ Allen, Thomas Hunt Morgan, pp 227-234
  25. ^ Allen, Garland E. (2009). Ruse, Michael; Travis, Joseph (eds.). Evolution. The First Four Billion Years. Harvard University Press. p. 746. ISBN 9780674031753.
  26. ^ "I think we shall be justified in rejecting it as an explanation of the secondary sexual differences amongst animals", page 220-221, chapter VI, Evolution and Adaptation, 1903.
  27. ^ Chapter VII of Evolution and Adaptation, 1903.
  28. ^ Bowler, Peter (2003). Evolution. The History of an Idea. University of California Press. chapter 7.
  29. ^ A Critique of the Theory of Evolution, Princeton University Press, 1916, p. 193-194
  30. ^ A Critique of the Theory of Evolution, page 189.
  31. ^ Kandel, Eric. 1999. "Genes, Chromosomes, and the Origins of Modern Biology", Columbia Magazine
  32. ^ George Pendle (2006). Strange Angel: The Otherworldly Life of Rocket Scientist John Whiteside Parsons. Houghton Mifflin Harcourt. p. 69. ISBN 9780156031790. The Nobel Prize-winning geneticist and stringent atheist Thomas Hunt Morgan was developing the chromosome theory of heredity by examining his swarm of mutated Drosophila (fruit flies) through a jeweler's loupe.
  33. ^ "Morgan's passion for experimentation was symptomatic of his general scepticism and his distaste for speculation. He believed only what could be proven. He was said to be an atheist, and I have always believed that he was. Everything I knew about him—his scepticism, his honesty—was consistent with disbelief in the supernatural." Norman H. Horowitz, T. H. Morgan at Caltech: A Reminiscence, Genetics, Vol. 149, 1629-1632, August 1998, Copyright © 1998.
  34. ^ Judith R. Goodstein. "The Thomas Hunt Morgan Era in Biology" (PDF). Calteches.library.caltech.edu. Retrieved 28 April 2019.
  35. ^ Horowitz, Norman H. (1 August 1998). "T. H. Morgan at Caltech: A Reminiscence". Genetics. 149 (4): 1629–1632. PMID 9691024.

Further reading

External links

Alfred Sturtevant

Alfred Henry Sturtevant (November 21, 1891 – April 5, 1970) was an American geneticist. Sturtevant constructed the first genetic map of a chromosome in 1911. Throughout his career he worked on the organism Drosophila melanogaster with Thomas Hunt Morgan. By watching the development of flies in which the earliest cell division produced two different genomes, he measured the embryonic distance between organs in a unit which is called the sturt in his honor. In 1967, Sturtevant received the National Medal of Science.

Barbara J. Meyer

Barbara J. Meyer (born 1949) is a biologist, noted for her pioneering research on lambda phage, a virus that infects bacteria; discovery of the master control gene involved in sex determination; and studies of gene regulation, particularly dosage compensation.

Bead theory

The bead theory is a disproved hypothesis that genes are arranged on the chromosome like beads on a necklace. This theory was first proposed by Thomas Hunt Morgan after discovering genes through his work with breeding red and white eyed fruit flies. According to this theory, the existence of a gene as a unit of inheritance is recognized through its mutant alleles. A mutant allele affects a single phenotypic character, maps to one chromosome locus, gives a mutant phenotype when paired and shows a Mendelian ratio when intercrossed. Several tenets of the bead theory are worth emphasizing :-

1. The gene is viewed as a fundamental unit of structure, indivisible by crossing over. Crossing over take place between genes ( the beads in this model ) but never within them.

2. The gene is viewed as the fundamental unit of change or mutation. It changes in toto from one allelic form into another; there are no smaller components within it that can change.

3. The gene is viewed as the fundamental unit of function ( although the precise function of gene is not specified in this model ). Parts of a gene, if they exist cannot function. Guido Pontecorvo continued to work under the basis of this theory until

Seymour Benzer showed in the 1950s that the bead theory was not correct. He demonstrated that a gene can be defined as a unit of function. A gene can be subdivided into a linear array of sites that are mutable and that can be recombined. The smallest units of mutation and recombination are now known to be correlated with single nucleotide pairs.

Bruce Ames

Bruce Nathan Ames (born December 16, 1928) is an American biochemist. He is a professor of Biochemistry and Molecular Biology Emeritus at the University of California, Berkeley, and a senior scientist at Children's Hospital Oakland Research Institute (CHORI). He is the inventor of the Ames test, a system for easily and cheaply testing the mutagenicity of compounds.

Don Melnick

Don J. Melnick (1953/1954 – April 18, 2019) was an environmental biologist and conservationist. He held the position of Thomas Hunt Morgan Professor of Conservation Biology at Columbia University, where he was also professor of anthropology and biological sciences.

He served as the founding Executive Director of the Center for Environmental Research and Conservation (CERC), a consortium of organizations including Columbia, the American Museum of Natural History, the New York Botanical Garden, the Wildlife Conservation Society, and the EcoHealth Alliance. He also served as co-chair of the United Nations Millennium Task Force on Environmental Sustainability, charged with reporting on the Millennium Development Goals for global environmental sustainability to the Secretary General.

Melnick received his Ph.D. in Physical Anthropology from Yale in 1981, and became one of Columbia's youngest tenured faculty members, as well as the youngest person ever to serve as chair of Columbia's Anthropology Department. For six years (1987-1993), he lived in one of Columbia's undergraduate dormitories as faculty-in-residence. He died at the age of 65 in 2019.

Edward B. Lewis

Edward Butts Lewis (May 20, 1918 – July 21, 2004) was an American geneticist, a corecipient of the 1995 Nobel Prize in Physiology or Medicine. He helped to found the field of evolutionary developmental biology.

Evelyn M. Witkin

Evelyn M. Witkin, born Evelyn Maisel (born March 9, 1921) is an American geneticist who was awarded the National Medal of Science for her work on DNA mutagenesis and DNA repair.

Fernandus Payne

Fernandus Payne (February 13, 1881 – October 13, 1977) was an American zoologist, geneticist and educator.

Panye was born in Shelbyville, Indiana. He received a B.Sc. from Valparaiso University in 1901 and a B.A. from Indiana University in 1905, and a M.A. in 1906. He undertook graduate studies at Columbia University with Thomas Hunt Morgan, his research took place when the use of fruit fly Drosophila melanogaster was being established in Morgan's lab. One of Payne's projects was to breed flies in the dark, if a generation of blind flies was produced then a model of Lamarckism would be confirmed. After producing 69 generation of flies grown in the dark Payne failed to produce a blind fly. Payne also helped Morgan produce X-ray mutagenised flies, these were used for many years to come in Morgans lab. Payne completed his PhD in 1909.

Payne returned to Indiana University where he was made associate professor. He remained at the University for the remainder of his career, he was credited with introducing genetics to the University and attracting other researchers to IU like Hermann Joseph Muller and Salvatore Luria who both became Nobel laureates.

Asteroid 2496 Fernandus, discovered October 8, 1953 by the Indiana Asteroid Program, is named for him.

He also served on the board of trustees for Science Service, now known as Society for Science & the Public, from 1953-1954.

Garland E. Allen

Garland Edward Allen III (born February 13, 1936) is an American historian and biographer at Washington University in St. Louis. His research interests lie primarily in the history of genetics, eugenics and evolution.

Hunt–Morgan House

The Hunt–Morgan House, historically known as Hopemont, is a Federal style residence in Lexington, Kentucky built in 1814 by John Wesley Hunt, the first millionaire west of the Alleghenies. The house is included in the Gratz Park Historic District. The Alexander T. Hunt Civil War Museum is located on the second floor of the Hunt–Morgan House.Other notable people who resided at Hopemont include John Wesley Hunt's grandson, General John Hunt Morgan, a general in the Confederate Army. Dr. Thomas Hunt Morgan, the first Kentuckian to win the Nobel Prize, was born in the house in 1866.

The House has many beautiful architectural features, including the Palladian window with fan and sidelights that grace its front façade. In 1955 the Blue Grass Trust for Historic Preservation was formed to save this home from impending demolition. The organization restored the home to its Federal appearance.The Hunt–Morgan House is located on the corner of Mill and Second Streets, at 201 N. Mill Street, in Gratz Park in Lexington.

The Bluegrass Trust for Historic Preservation still maintains the Hunt-Morgan House. In addition to providing tours, they also host events, including art shows and weddings.

Isabel Morgan

Isabel Merrick Morgan (also Morgan Mountain) (20 August 1911 – 18 August 1996) was an American virologist at Johns Hopkins University who prepared an experimental vaccine that protected monkeys against polio in a research team with David Bodian and Howard A. Howe. She was the daughter of Thomas Hunt Morgan and Lilian Vaughan Sampson.

Kerckhoff Marine Laboratory

The William G. Kerckhoff Marine Laboratory is owned and operated by the California Institute of Technology. It is located 101 Dahlia Street, in the Corona del Mar district of Newport Beach, in Orange County, California.

HistoryThe marine laboratory was established by biologist Thomas Hunt Morgan in 1928 to replicate the facilities at the Stazione Zoologica in Naples, Italy. Caltech made the decision to purchase the facility in 1929. It is one of the oldest marine laboratories on the West Coast of the United States. From 1962 until his death in 2002, Dr. Wheeler J. North conducted numerous studies on the ecology of the California kelp forests while based at this laboratory. During the 1990s and 2000s investigators included members of the Eric Davidson lab working on various marine biology related projects.The facility fell into disuse by the early 2010s, as Caltech no longer maintained an oceanography research program. In 2015, Caltech and UC Irvine began talks to revitalize the facility as a shared laboratory to support UC Irvine's marine science programs.

List of Fellows of the Royal Society elected in 1919

This is a list of Fellows of the Royal Society elected in 1919.

Mendelian inheritance

Mendelian inheritance is a type of biological inheritance that follows the laws originally proposed by Gregor Mendel in 1865 and 1866 and re-discovered in 1900. These laws were initially controversial. When Mendel's theories were integrated with the Boveri–Sutton chromosome theory of inheritance by Thomas Hunt Morgan in 1915, they became the core of classical genetics. Ronald Fisher combined these ideas with the theory of natural selection in his 1930 book The Genetical Theory of Natural Selection, putting evolution onto a mathematical footing and forming the basis for population genetics within the modern evolutionary synthesis.

Nettie Stevens

Nettie Maria Stevens (July 7, 1861 – May 4, 1912) was an early American geneticist credited with the discovery of sex chromosomes. In 1905, soon after the rediscovery of Mendel's paper on genetics in 1900, she observed that male mealworms produced two kinds of sperm, one with a large chromosome and one with a small chromosome. When the sperm with the large chromosome fertilized eggs, they produced female offspring, and when the sperm with the small chromosome fertilized eggs, they produced male offspring. The pair of sex chromosomes that she studied later became known as the X and Y chromosomes.

Thomas Hunt Morgan Medal

The Thomas Hunt Morgan Medal is awarded by the Genetics Society of America (GSA) for lifetime contributions to the field of genetics.

The medal is named after Thomas Hunt Morgan, the 1933 Nobel Prize winner, who received this award for his work with Drosophila and his "discoveries concerning the role played by the chromosome in heredity." Morgan recognized that Drosophila, which could be bred quickly and inexpensively, had large quantities of offspring and a short life cycle, would make an excellent organism for genetic studies. His studies of the white-eye mutation and discovery of sex-linked inheritance provided the first experimental evidence that chromosomes are the carriers of genetic information. Subsequent studies in his laboratory led to the discovery of recombination and the first genetic maps.

In 1981 the GSA established the Thomas Hunt Morgan Medal for lifetime achievement to honor this classical geneticist who was among those who laid the foundation for modern genetics.

Thomas Hunt Morgan bibliography

This is a list of books and monographs by the American geneticist Thomas Hunt Morgan. Morgan produced 22 books on embryology, genetics and evolution. Books are in order by date. Three of Morgan's co-authors have their own articles: Calvin Bridges, Alfred Sturtevant and Hermann Joseph Muller.

The Development of the Frog's Egg: An Introduction to Experimental Embryology, New York: Macmillan, 1897. Full text online at [1]. Translated into German by Bernhard Solger and published in 1904 as Die Entwicklung des Froscheies.[2].

Regeneration Columbia University Biological Series, New York: Macmillan, 1901. Full text online at [3].

Evolution and Adaptation, New York: Macmillan, 1903. Full text online at [4].

Experimental Zoology, New York: Macmillan, 1907

Heredity and Sex, New York: Columbia University Press, 1913. Full text online at [5].

The Mechanism of Mendelian Heredity, with A.H. Sturtevant, H.J. Muller and C.B. Bridges, New York:Henry Holt, 1915. Revised and re-issued in 1922. Full text online at [6].

A Critique of the Theory of Evolution, Princeton NJ: Princeton University Press, 1916. Full text online at [7].

Sex-linked Inheritance in Drosophila, with C.B. Bridges, Washington DC: Carnegie Institution, 1916. Full text online at [8].

The Genetic and the Operative Evidence of Relating to Secondary Sexual Characteristics, Washington DC: Carnegie Institution, 1919

The Physical Basis of Heredity, Monographs on Experimental Biology, Philadelphia: J.B. Lippincott, 1919. Full text online at [9].

Contributions to the Genetics of Drosophila Melanogaster, with A.H.Sturtevant and C.B.Bridges: Carnegie Institution of Washington, 1919.

Some Possible Bearings of Genetics on Pathology, Lancaster PA: New Era Printing Co., 1922

The Third-Chromosome Group of Mutant Characters of Drosophila melanogaster, with C.B. Bridges, Washington DC: Carnegie Institution, 1923

Laboratory Directions for and Elementary Course in Genetics, with H.J. Muller, A.H. Sturtevant and C.B. Bridges, New York: Henry Holt, 1923

Human Inheritance, Pittsburgh:University of Pittsburgh School of Medicine, 1924

Evolution and Genetics, Princeton NJ: Princeton University Press, 1925

The Theory of the Gene, New Haven: Yale University Press, 1926

Genetics and the Physiology of Development, Woods Hole: Marine Biological Laboratory, 1926

Experimental Embryology, New York: Columbia University Press, 1927

What is Darwinism?, New York: W.H. Norton, 1929

The Scientific Basis of Evolution, New York: W.H. Norton, 1932

Embryology and Genetics, New York: Columbia University Press, 1934

VASKhNIL

VASKhNIL (Russian: ВАСХНИЛ) was the All-Union Academy of Agricultural Sciences of the Soviet Union (the acronym stands for "Lenin All-Union Academy of Agricultural Sciences" or "V.I. Lenin Academy of Agricultural Sciences," "Всесоюзная академия сельскохозяйственных наук имени В. И. Ленина"). Built upon the model of the Academy of Sciences of USSR, VASKhNIL included not only a body of academicians but a vast network of research institutions scattered all over the country with thousands of researchers, plant and cattle breeders.

It operated from 1929 to 1992 (dissolution of the Soviet Union). In the 1930s - 1940s, meetings of the academy members ("sessions" of VASKhNIL) provided the floor for debates between Lysenkoists and geneticists. After Trofim Lysenko had taken control over the Academy, it became for about thirty years a stronghold of Lysenkoism. The proverbial among Russian biologists "August session of VASKhNIL" (July 31 - August 7, 1948) organised under control of the Communist party (Joseph Stalin personally corrected the drafts of the Trofim Lysenko's opening address "On the Situation in Biological Science") led to a formal ban on teaching "Mendelist-Weismannist-Morganist" genetics (a pejorative label based on the names of Gregor Mendel, August Weismann, and Thomas Hunt Morgan), which was effective until the early 1960s.

White (mutation)

white, abbreviated w, was the first sex-linked mutation discovered, found in the fruit fly Drosophila melanogaster. In 1910 Thomas Hunt Morgan and Lilian Vaughan Morgan collected a single male white-eyed mutant from a population of Drosophila melanogaster fruit flies, which usually have dark brick red compound eyes. Upon crossing this male with wild-type female flies, they found that the offspring did not conform to the expectations of Mendelian inheritance. The first generation (the F1) produced 1,237 red-eyed offspring and three white-eyed male flies. The second generation (the F2) produced 2,459 red-eyed females, 1,011 red-eyed males, and 782 white-eyed males. Further experimental crosses led them to the conclusion that this mutation was somehow physically connected to the "factor" that determined sex in Drosophila. This led to the discovery of sex linkage, in which the gene for a trait is found on a sex chromosome. Morgan named this trait white, now abbreviated w. Flies possessing the white allele are frequently used to introduce high school and college students to genetics.

Recipients of the Copley Medal (1901–1950)
1901–1925
1926–1950
1951–1975
1976–2000
2001–present

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