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Profile of Barbara McClintock

written by: Jessica Gross•edited by: Paul Arnold•updated: 9/3/2009

Barbara McClintock (1902-1992), who focused on maize genetics, studied the transposition of genes on chromosomes during breeding. McClintock won awards throughout her career, culminating in the 1983 Nobel Prize in Physiology or Medicine. Her insights were decades ahead of many of her contempories.

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    Barbara McClintock's Important Work

    Genetics researcher Barbara McClintock's (1902-1992) 1983 Nobel Prize rewarded her discovery of genetic transposition in maize. Though McClintock didn't receive the Nobel Prize until her eighties, she won honors for her groundbreaking genetics research throughout her career and was a world famous geneticist in her time. She was elected to the National Academy of Sciences in 1944, became the Genetics Society of America's first female president one year later, was awarded the National Medal of Science in 1971, and won the first MacArthur Foundation Grant, or "genius grant," in 1981.

    McClintock's career was auspicious from the start. She received her B.S., M.S. and Ph.D.—all in botany—from Cornell University. She was barred from majoring in genetics, closed to women at the time. But in the 1938s, she won several fellowships that allowed her to research genetics at universities across the United States. McClintock subsequently taught as an assistant professor at the University of Missouri at Columbia beginning in 1936 and joined the Carnegie Institution of Washington's Department of Genetics at New York's Cold Spring Harbor in late 1941, where she remained until her retirement in 1967.

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    Genetic Transposition

    What is genetic transposition, that process whose discovery earned McClintock her 1983 Nobel Prize? The name tells the story: "trans" signifies change; transposition is a change in position. McClintock's major discovery was that genes can move around on chromosomes—they become detached from the DNA, then reinsert into a different spot.

    McClintock's transposition research is her most famous, but it was more a jumping-off point than an endpoint for her. At Cold Spring Harbor, McClintock discovered two genetic loci, "Dissociator" and "Activator." Dissociator affected neighboring genes' expression—but only in Activator's presence. And both could transpose. That explained why an organism with the same genetic material in every cell could develop tissues and other parts with divergent qualities. It all depended on which genes were being expressed, which in turn depended on where Dissociator (the gene activator), was located. If Dissociator moved, it affected different genes. So transposition, for McClintock, answered the broader question of why organisms could use the same genes to produce differential physical properties.

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    Transposition Today

    In the past several decades, scientists have built on McClintock's work with transposition. In the 1970s, biologists studying bacteria and viruses found transposition in their genetic structures; later, researchers found that yeast employed transposition as well. Today, some transposons—the pieces of DNA that change position within genomes, of which McClintock's Dissociator is an example—are used to produce mutations. By inserting into a piece of DNA and mutating a neighboring gene, these transposons can enable adjacent cells to have different genotypes.

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