Location of an X-linked factor causing sterility in male hybrids of Drosophila simulans and D. mauritiana.

We report the first mapping of a genetic factor responsible for reproductive isolation: a small segment of genome strongly affecting sperm motility in hybrids between the sibling species Drosophila simulans and D. mauritiana. Maximum-likelihood analysis of data from ten generations of backcrossing places this factor at 1.1 +/- 0.2 map units from the forked locus, at position 54.9 +/- 0.2 or 57.1 +/- 0.2 on the X chromosome.