Today is the birthday of Barbara McClintock (June 16, 1902 – September 2, 1992). She was the first woman to win a Nobel Prize unshared in Physiology and Medicine, and the first American woman to win any Nobel Prize unshared.
She discovered Transposomes and Mosaicism in Genetics and with that new pathways for genetic recombination in animals and plants. With this, and her subsequent description of the lac operon, she essentially decoded genetic regulation.