MUTATION AND EVOLUTION OF MICROSATELLITES IN DROSOPHILA-MELANOGASTER

Levels of nucleotide polymorphism in the Drosophila melanogaster genom e are correlated with rates of recombination. This relationship may be due to hitchhiking of advantageous mutations (selective sweeps) or to continual removal of deleterious mutations from the genome (backgroun d selection). One test of the relative contributions of selective swee ps and background selection to the observed levels of variation in the genome of D. melanogaster is to compare levels of nucleotide variabil ity (with a mutation rate on the order of 10(-9) per nucleotide per ge neration) with more rapidly evolving DNA loci such as microsatellites. This test depends critically on details of the mutational process of microsatellites. In this paper, we summarize our studies of microsatel lite characteristics and mutation rates in D, melanogaster. We find th at D, melanogaster microsatellites are short and have a mutation rate (6.5 x 10(-6) per locus per generation) several orders of magnitude lo wer than mammals studied to date. We further show that genetic variati on at 18 dinucleotide repeat microsatellites in a population of D. mel anogaster from Maryland is correlated with regional rates of recombina tion. These and other microsatellite data suggest that both background selection and selective sweeps may contribute to the correlation betw een DNA sequence variation and recombination in Drosophila.