The unexpected recovery of hybrids in a Drosophila species cross: a genetic analysis.

The species cross between Drosophila melanogaster and D. simulans was first described by Sturtevant in the 1920s. According to his description, the hybridization of D. simulans females and D. melanogaster males produces only (or almost only) male progeny. Female hybrids are embryonic lethal. Here it is shown that these traditional results no longer hold. Instead, D. simulans is polymorphic for factor(s) that qualitatively affect the outcome of species crosses to D. melanogaster. Remarkably, many, if not most, strains of D. simulans produce abundant female hybrids when crossed to D. melanogaster males. Genetic analysis of the difference between D. simulans strains that produce many versus few hybrid females shows that recovery of hybrid females depends on autosomal, maternally acting gene(s).