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Barbara McClintock (June 16, 1902 – September 2, 1992) was a pioneering American scientist and one of the world's most distinguished cytogeneticists. McClintock received her PhD in botany from Cornell University in 1927, where she was a leader in the development of maize cytogenetics. The field remained the focus of her research for the rest of her career. From the late 1920s, McClintock studied chromosomes and how they change during reproduction in maize. She developed the technique to visualize maize chromosomes and demonstrate genetic recombination by crossing-over during meiosis—a mechanism by which chromosomes exchange information. She produced the first genetic map for maize, and she demonstrated the role of the telomere and centromere. She was awarded prestigious fellowships and elected a member of the National Academy of Sciences in 1944.