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 t he continuous activity of the sex-determining gene F from early embryo genesis until metamorphosis. To activate F in embryogenesis, two condi tions must be met There must be no male-determining M factor in the zy gotic genome, and the egg must be preconditioned by F activity in the maternal germ line. This maternal activity can be suppressed by introd ucing an M factor into the maternal germ line, which causes all offspr ing, including those that do not carry M to develop as males. By trans plantation of pole cells (germline progenitor cells) we have construct ed such females with a genetically male germ line and, simultaneously, males with a genetically female germ line carrying a constitutive all ele off [F-Dominant (F-D)]. Crosses between these animals yielded offs pring 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. Thi s shows that zygotic F function alone is sufficient to promote female development and that in the wild-type situation, maternal F product se rves no other function but to activate the zygotic F gene.