Barbara McClintock

McClintock earned her PhD in botany from Cornell in 1927 and built maize cytogenetics from the ground up, developing techniques to visualize chromosomes under the microscope. Through the late 1920s and 1930s she demonstrated genetic recombination during meiosis and identified the functions of telomeres and centromeres - work so sharp she was elected to the National Academy of Sciences in 1944. In the 1940s and 1950s she discovered transposons and showed that genes could regulate themselves across generations, but skepticism of her findings drove her out of publication by 1953. She spent years studying maize races in South America while the rest of molecular biology caught up. By the 1960s and 1970s other scientists confirmed what she'd shown decades earlier, and in 1983 she received the Nobel Prize in Physiology or Medicine - unshared, the only woman in that category to this day.