Why was it not necessary to isolate virgin females for the F1 cross?
It was not necessary to isolate the virgin females because they are virgins and therefore don't have sperm in their receptacles. It'd be pointless to isolate them because it is the virgins we need for the experiment. They have just hatched and so we know for a fact they are virgins. Also, the male flies they were exposed to were also of the F1 generation. So, we'd not have to isolate them because the traits are the ones we are willing to cross