Male fertility in a female-sterile mutant of Drosophila melanogaster

The fertility and the fecundity of males homozygous for the recessive female-sterile factor fs(2)TLM have been investigated. Both for standard mating and for observed mating procedures, there was a more than 35% male sterility. Moreover, in a total fecundity experiment the fertile males (about 70%) were effectively fertile for a shorter time than the control males, and the mean progeny per male was about a third that of the controls. It can thus be concluded that the penetrance of the fs(2)TLM factor is different in the two sexes, being complete in the females and incomplete (0.35) in the males. Furthermore, in the males it shows two different degrees of expressivity: complete sterility and fecundity lowered by about 70%. It is suggested that the resultant sterility of these males is a consequence not merely of altered processes causing testicular abnormalities, but also of independent events directly affecting spermatogenesis.