When males from certain outside strains are mated to lab females, the hybrid progeny are only partially sterile rather than completely sterile. Given this information, describe crosses that would allow you to isolate loss-of-function mutations in the X-linked Drosophila gene yellow that are caused by P element insertion. (These recessive mutant alleles will produce yellow rather than the wild-type tan body color.) At the molecular level, what do you think explains the difference between outside strains whose hybrid progeny are all sterile and outside strains who's progeny are only semi sterile