Chromosomal effects of rapid gene evolution in Drosophila melanogaster

Rapid adaptive fixation of a new favorable mutation is expected to affect n eighboring genes along the chromosome. Evolutionary theory predicts that th e chromosomal region would show a reduced level of genetic variation and an excess of rare alleles, We have confirmed these predictions in a region of the X chromosome of Drosophila melanogaster that contains a newly evolved gene far a component of the sperm axoneme. In D, simulans, where the novel gene does not exist, the pattern of genetic variation is consistent with se lection against recurrent deleterious mutations. These findings imply that the pattern of genetic variation along a chromosome may be useful for infer ring its evolutionary history and for revealing regions in which recent ada ptive fixations have taken place.