What is the X in X-mas?
McClintock Mc·Clin·tock (mə-klĭn'tək, -tŏk'), Barbara. 1902-1992.
American genetic botanist. She won a 1983 Nobel Prize for discovering that genes are mobile within the chromosomes of a plant cell.
American geneticist who researched the chromosome theory of heredity and demonstrated how genes can control other genes and jump from chromosome to chromosome. These "jumping genes" were later called transposons. She was awarded the Nobel Prize for physiology or medicine in 1983.