The XY sex determination system was first described independently by Nettie Stevens and Edmund Beecher Wilson in 1905

Mechanisms Some species (including most mammals)

have a gene or genes on the Y chromosome that determine maleness. In the case of humans, a single gene (SRY) on the Y chromosome acts as a signal to set the developmental pathway towards maleness. Other mammals use several genes on the Y chromosome for that same purpose. Not all male-specific genes are located on the Y chromosome.