Role of the autosomes in the Drosophila pseudoobscura hybrids

Lancefield(1) discovered that the species Drosophila pseudoobscura consists of two races, called race A and race B, respectively. Completely sterile males and partially fertile females appear in the offspring if the races are intercrossed. Males coming from the cross, B♀ X A♂, have rudimentary testes that are smaller in size than the testes of normal males. Testes of the A♀ X B♂ hybrid males are normal in size but incapable of producing functional sperm.