McClintock, Barbara, 1902-1992

Barbara McClintock was a maize geneticist who discovered "crossing over" and translocation or "jumping genes." She received the Nobel Prize in Physiology or Medicine in 1983.

Barbara McClintock, a maize geneticist, was born in Hartford, Connecticut on 16 June 1902. In 1908 her family moved to Brooklyn, New York, where her interest in science began at Erasmus Hall High School. When she finished high school in 1919, McClintock enrolled, despite her parents' opposition, at Cornell University's College of Agriculture. Since the College would not allow women to major in plant breeding, McClintock majored in botany. At the end of her junior year, after having taken a genetics course, she was invited to take the graduate course in genetics and was unofficially made a graduate student. She received her B.A. in 1923, at which time approximately 25% of the graduates from the College of Agriculture were women. She went on to receive her Ph.D. in botany in 1927; her thesis advisor was Lester Sharp, a cytology professor in the Botany Department.

McClintock remained at Cornell doing research for another four years. Then, receiving a fellowship from the National Research Council, she studied and taught at the University of Missouri, California Institute of Technology, and Cornell University between 1931 and 1933. Cornell remained her home base, even though the University did not offer her a job. (The first woman assistant professor at Cornell in a field other than home economics was not appointed until 1947.) In 1933, McClintock received a Guggenheim Fellowship to study in Germany but returned within the year due to the depressed, troubled conditions in Germany. (The geneticist Curt Stern, with whom she had been planning to study, had already left the country.)

McClintock again did research at Cornell until 1936, working in Rollins Emerson's laboratory supported by the Rockefeller Foundation. That year, she moved to the University of Missouri at Columbia, where she was Assistant Professor of Botany until 1940. At that time, not having been offered an incentive to stay, she went to Cold Spring Harbor with Marcus Rhoades where she studied maize until the following November. In December 1941, when Milislav Demerec became Director of the Department of Genetics of the Carnegie Institution of Washington at Cold Spring Harbor, he offered her a one-year position, which was later made permanent. She remained Staff Member at the Carnegie Institution until 1967, when she became Distinguished Service Member.

During her tenure at the Carnegie Institution McClintock was also Consultant (from 1962 to 1969) to the Agricultural Science Program of the Rockefeller Foundation, which funded research in maize in South America. Much of this work involved discussing research results with, among others, Takeo A. Kato Yamakake and Almiro Blumenschein, with whom she later wrote a book, Chromosome Constitution of Races of Maize.

McClintock traced genes through the changes in the colored kernels of maize. In the 1930s she discovered "crossing over," in which chromosomes break and recombine to create genetic changes. In the 1950s, she discovered the occurrence of transposable genetic elements and their effect on gene expression; that is, that genes are not fixed like pearls on a string but that they move or "jump" around. She found the first jumping gene on the short arm of chromosome 9. Because the gene broke the chromosome into two parts, she called the gene "DS" or dissociation element. She called the jumping genes "control elements" because they inactivated neighboring genes on the chromosome. The element, which causes the gene to jump, she called "AC" or activator element.

McClintock's findings were ignored, partly because the complex development patterns of maize were not as clear to everyone else (especially non-maize geneticists) as they were to her. In the 1970s, molecular biologists isolated transposable elements in bacteria and discovered that they were used by cells to control genes, revealing the same discovery that McClintock had made twenty years earlier in maize.

In time, McClintock's work was appreciated and lauded. She received many awards for her research in maize, including an Award of Merit from the Botanical Society of America (1957), the Kimber Genetics Award from the National Academy of Science (1967), the National Medal of Science (1970), the Louis and Bert Freedman Foundation Award for Research in Biochemistry (1978), the John D. and Catherine T. MacArthur Foundation Prize (1978), the Lewis S. Rosenstiel Award (1978), the Albert Lasker Basic Medical Research Award (1981), the Wolf Foundation Award (1981), the Louisa Gross Horwitz Prize (1982), the Charles Leopold Mayer Prize (1982), and the Nobel Prize in Physiology or Medicine (1983). McClintock was the first woman to win an unshared Nobel Prize in that category and the third woman to win an unshared Nobel Prize in science.

McClintock also received numerous honorary degrees, including those from Georgetown University, Harvard University, University of Cambridge, and Yale University. She was a member of various societies, including the American Academy of Arts and Sciences, the American Association for the Advancement of Science, the American Institute of Biological Sciences, the American Philosophical Society, the American Society of Naturalists, the Botanical Society of America, the Genetics Society of America (by which she was elected Vice President in 1939 and the first woman President in 1945), the National Academy of Sciences (she was the third woman ever elected), the National Women's Hall of Fame, the New York Academy of Sciences, and the Royal Society of London.

Barbara McClintock died on 2 September 1992 at age ninety.