Female reproductive system
The female reproductive system develops based upon chromosome characteristics at conception. The mother's egg contains an X chromosome and the father's sperm contains either an X or Y chromosome. It is the male who determines the fetus's sex. If the fetus inherits the X chromosome from the father, the fetus will be a female. Testosterone is not made and the fetus develops female sex organs.  If the fetus inherits the Y chromosome from the father, the fetus will be a male. The presence of testosterone in the embryo will stimulate the development of the male sex organs.