Crossing in fruit flies?

when gray bodied female fruit flies are crossed with yellow bodied male fruit flies, the resulting F1 generation is gray. when the reciprocal of this cross (yellow females x gray males) is performed, the F1 females are again gray, but the F1 males are yellow. explain these results. include punnett squares showing the gametes produced by the parents and the genotypes expected in the F1 generation for each of these crosses.