Abstract
A male-sterile mutant, ms(1)7, of Drosophila melanogaster is defective in post-ejaculatory sperm function. The mutant gene is located at one of at least five male fertility loci in 18F through section 20 of the polytene X-chromosome. It is proposed that the ms(1)7+ gene product modifies a component of the sperm head. A nearby gene may be functionally related to ms(1)7+.