Edmund Beecher WilsonDied 3 Mar 1939 at age 82 (born 19 Oct 1856). American biologist known for his researches in embryology and cytology. His first experimental studies, in embryology, led him to investigations at the cellular level. His principal work was on the function of the cell in heredity and showed the chromosomal basis of sex determination in the embryo (1905). Wilson concluded that females have XX chromosomes, while males possess XY chromosomes. Following the process of meiosis, all eggs are left with an X chromosome, but sperm can have either X or Y. If an X chromosome sperm fertilizes an egg, the result is a female. If a Y chromosome sperm fertilizes and egg, the result is a male. He was the first scientist to publish photographs illustrating how a cell divides.