Effects of the fourth chromosome on the sterility of hybrids between Drosophila simulans and its relatives.

Genetic analysis of the fourth chromosome of Drosophila simulans shows that it has no effect on either male or female fertility in hybrids with two sibling species, D. mauritiana and D. sechellia. The lack of effect holds even when the D. simulans chromosome is homozygous in a foreign genetic background. The absence of major fourth chromosome "sterility genes" in these hybridizations contrasts with the presence of a fourth-chromosome gene causing complete male sterility in hybrids of the more distantly related species D. melanogaster and D. simulans.