It appeared to him as if the females were developing male sex organs. Vainio speculated that mutant Wnt-4 genes were masculinizing the females. McMahon, his boss, wouldn't buy it. But I let him pursue the idea. McMahon remained skeptical and Vainio continued the pursuit for three years.
All mammals probably share the same genetic requirements for reproductive development.
Vainio, McMahon, and their colleagues reported their conclusions in the Feb. 4 issue of the journal Nature . Starting Out Male and Female Mice and humans start out having both male and female reproductive systems, and both have master genes that guide their development. The winner determines sex. When it functions normally, the gene suppresses the male sex system by preventing production of the hormone testosterone. At the same time, Wnt-4 initiates development of the M llerian duct, which gives rise to the oviduct, uterus, and upper vagina.