Selective sweep at the Drosophila melanogaster Suppressor of Hairless locus and its association with the In(2L)t inversion polymorphism

The hitchhiking model of population genetics predicts that an allele favore d by Darwinian selection can replace haplotypes from the same locus previou sly established at a neutral mutation-drift equilibrium. This process, know n as "selective sweep," was studied by comparing molecular variation betwee n the polymorphic In(2L)t inversion and the standard chromosome. Sequence v ariation was recorded at the Suppressor of Hairless (Su[H]) gene in an Afri can population of Drosophila melanogaster. We found 47 nucleotide polymorph isms among 20 sequences of 1.2 kb. Neutrality tests were nonsignificant at the nucleotide level. However, these sites were strongly associated, becaus e 290 out of 741 observed pairwise combinations between them were in signif icant linkage disequilibrium. We found only seven haplotypes, two occurring in the 9 In(2L)t chromosomes, and five in the 11 standard chromosomes, wit h no shared haplotype. Two haplotypes, one in each chromosome arrangement, made up two-thirds of the sample. This low haplotype diversity departed fro m the neutrality in a haplotype test. This pattern supports a selective swe ep hypothesis for the Su(H) chromosome region.