Zygotically rescues the embryonic lethality of female progeny of a cross between D.simulans females and D.melanogaster males, but does not rescue the female progeny of a cross between D.mauritiana or D.sechellia females and D.melanogaster males. If parts of the D.mauritiana or D.sechellia chromosomes are replaced homozygously by D.simulans chromosomal material, then the female progeny of a cross between D.mauritiana or D.sechellia females and D.melanogaster males are rescued.