The female-determining gene F of the housefly, Musca domestica, acts maternally to regulate its own zygotic activity.

In Musca domestica, the common housefly, female development requires the continuous activity of the sex-determining gene F from early embryogenesis until metamorphosis. To activate F in embryogenesis, two conditions must be met: There must be no male-determining M factor in the zygotic genome, and the egg must be preconditioned by F activity in the maternal germ line. This maternal activity can be suppressed by introducing an M factor into the maternal germ line, which causes all offspring, including those that do not carry M, to develop as males. By transplantation of pole cells (germline progenitor cells) we have constructed such females with a genetically male germ line and, simultaneously, males with a genetically female germ line carrying a constitutive allele of F [F(Dominant) (F(D))]. Crosses between these animals yielded offspring that, despite the presence of M in the maternal germ line, were of female sex, solely due to zygotic F(D) brought in via the sperm. This shows that zygotic F function alone is sufficient to promote female development and that in the wild-type situation, maternal F product serves no other function but to activate the zygotic F gene.