The theory of Nettie Stevens
In 1905, Nettie Stevens discovered that biological sex is determined by specific chromosomes (X and Y), revolutionizing our understanding of human heredity.
Explanation and Popularization of Her Discovery (XY Sex Chromosomes)
Nettie Stevens discovered, while studying insects, that biological sex is determined by a difference in chromosomes. She observed that females have two X chromosomes, while males have one X and one Y. Therefore, the combination of these chromosomes inherited from the parents determines an individual’s sex. This discovery was the first proof that sex is set by chromosomes, not by the environment or diet, as previously thought.
Associated Illustrations/Diagrams
This size difference is visible under a microscope.
Nettie Stevens used special staining techniques to make the chromosomes visible. She examined hundreds of cells to confirm that the Y chromosome was consistently smaller in all males.
