Evolution caught in the act

Duplication, deletion and mutation have created a new gene, denoted Sdic, that encodes a fly sperm axoneme protein. Sdic is present in the fly Drosophila melanogaster, but not in its close relative Drosophila simulans. In the 5 January Science, Nurminsky et al. find evidence for a selective sweep around Sdic in D. melanogaster (Science 2001, 291:128-130). D. melanogaster DNA has a significant depression in the level of synonymous polymorphism around Sdic, and an increase in the occurrence of rare alleles, including singletons. In contrast, D. simulans DNA has a smooth distribution of polymorphisms in the equivalent region. The pattern in D. melanogaster suggests that strong selection and evolution is ongoing, displacing linked polymorphisms in the process. A similar analysis may be useful for identifying the locations of other recently selected genes.