'Exceptional sons' from Drosophila melanogaster mothers carrying a balancer X chromosome

This study reports on exceptional males which are obtained by using Drosophila melanogaster mothers carrying the balancers In(1)FM6 or In(1)FM7 as one of their X chromosomes. The phenomenon was first observed in interspecific crosses between D. melanogaster females and males of its closest relatives which normally produce unisexual female hybrid progeny. Whereas hybrid sons from these crosses die as third instar larvae, the presence of the particular X balancers in the mother allows a low percentage of sons to survive. Similar sterile males are also observed among non-hybrid flies. Data are presented which suggest that the males thus generated could be hyperploid for part of their X chromosome as a result of a meiotic event in their mothers or else they could start life as female zygotes and change sex through a mitotic event at an early stage.