Nettie Stevens was an American geneticist born on July 7, 1861, in Cavendish, Vermont. She is best known for her pioneering work in the field of genetics, particularly her discovery of the sex chromosomes. Stevens conducted experiments on mealworms and identified that the presence of specific chromosomes determined the sex of an organism. In 1905, Stevens published her findings, which contributed significantly to the understanding of heredity and sex determination. Her work laid the foundation for future research in genetics and helped establish the importance of chromosomes in biological processes. Stevens' contributions are recognized as a crucial part of the history of genetics.