Barbara McClintock was an American scientist and cytogeneticist. She earned her PhD in botany from Cornell University in 1927 and became a leader in the development of maize cytogenetics. McClintock studied chromosomes and how they change during maize reproduction. She developed the technique for visualizing maize chromosomes, using microscopic analysis to demonstrate numerous fundamental genetic ideas. One of those ideas was the notion of jumping genes—genetic recombination by crossing-over during meiosis that allowed chromosomes to exchange information. She produced the first genetic map for maize, linking regions of the chromosome to physical traits. She demonstrated the role of the telomere and centromere, regions of the chromosome that are important in the conservation of genetic information. She was recognized among the best in the field, awarded prestigious fellowships, and elected a member of the National Academy of Sciences in 1944.
During the 1940s and 1950s, McClintock discovered transposition and used it to demonstrate that genes are responsible for turning physical characteristics on and off. She developed theories to explain the suppression and expression of genetic information from one generation of maize plants to the next. Due to skepticism of her research and its implications, she stopped publishing her data in 1953.
It wasn't until the 1960s and 1970s that McClintock's research became well understood, as other scientists confirmed the mechanisms of genetic change and genetic regulation that she had demonstrated in her maize research twenty years before. As a result, she won the Nobel Prize in Physiology or Medicine in 1983 for the discovery of genetic transposition. She is the only woman to receive an unshared Nobel Prize in that category.