Nettie Stevens

Nettie Maria Stevens (July 7, 1861 - May 4, 1912) was an American geneticist and biologist best known for discovering the chromosomal basis of sex. Through her research on insects, particularly mealworms, she identified that the X and Y sex chromosomes determine an organism's sex, overturning earlier theories that attributed sex determination to environmental or maternal influences. Her work was crucial in the development of modern genetics and laid the foundation for understanding sex-linked inheritance.