William Bateson was one of the pivotal figures in the early history of genetics, having championed the promise of Mendelism to unravel the secrets of heredity. Many refer to the "school" of genetics he directed at Cambridge between 1900 and 1910, but few note that Bateson's group consisted primarily of women. Bateson turned to botanists, zoologists, and physiologists associated with Newnham College, Cambridge, for critical assistance in advancing his research program at a time when Mendelism was not yet recognized as a legitimate field of study. Cambridge women carried out a series of breeding experiments in a number of plant and animal species between 1902 and 1910, the results of which provided crucial evidence that both supported and extended Mendel's laws of heredity. This essay shows how the situation of women in science in the early twentieth century was a factor--along with scientific, institutional, social, and political developments--in establishing the new discipline of genetics.