Women weren't allowed to major in genetics when Barbara McClintock attended Cornell, so she earned her PhD in botany instead.
Working on the chromosomal activity of maize in the '40s and '50s, she discovered genetic transposition, proving that genes turn physical characteristics on and off.
Initially met with skepticism, her work was confirmed in the '60s and '70s; she won the Nobel Prize in Physiology or Medicine in 1983.
https://www.energy.gov/articles/five-fast-facts-about-barbara-mcclintock
graphic: Cort Kreer

