Partial sweeping of variation at the Fbp2 locus in a West African population of Drosophila melanogaster

Departure of molecular variation from neutral equilibrium was studied in a highly recombining region of the Drosophila genome. A 2.2-kb region includi ng the Fbp2 locus was sequenced for 10 chromosomes from a D. melanogaster s ample from West Africa and for the related species D. simulans. Of the 33 v ariable sites present in the 1.3-kb transcription unit, 32 made up a single haplotype present in half of the D. melanogaster sample. This pattern sign ificantly departed from predictions of the neutral drift-mutation equilibri um model. The major haplotype presented a diagnostic restriction site which was investigated in 226 chromosomes from three distant European and Africa n populations. It was found at a high frequency (31%) in the population fro m which the sequenced sample originated, but was nearly absent from the oth er two (below 4%), suggesting that the major haplotype frequency resulted f rom a local selective sweep event. Partial sweeping of variation in regions of high recombination rates has previously been found for American and Eur opean populations of D. melanogaster: Our study shows that this phenomenon also occurs in African populations, which are in the ancestral range of thi s species.