Evidence of gene conversion associated with a selective sweep in Drosophila melanogaster.

Since Drosophila melanogaster colonized Europe from tropical Africa 10 to 15 thousand years ago, it is expected that adaptation has played a major role in this species in recent times. A previously conducted multilocus scan of noncoding DNA sequences on the X chromosome in an ancestral and a derived population of D. melanogaster revealed that some loci have been affected by directional selection in the European population. We investigated if the pattern of DNA sequence polymorphism in a region surrounding one of these loci can be explained by a hitchhiking event. We found strong evidence that the studied region around the gene unc-119 was shaped by a recent selective sweep, including a valley of reduced heterozygosity of 83.4 kb, a skew in the frequency spectrum, and significant linkage disequilibrium on one side of the valley. This region, however, was interrupted by gene conversion events leading to a strong haplotype structure in the center of the valley of reduced variation.