Hitchhiking and associative overdominance at a microsatellite locus

The possible effects of a selected locus on a closely linked microsatellitelocus are discussed and analyzed in terms of coalescent theory and modelsof the mutation process. Background selection caused by recurrentdeleterious mutations will reduce the variance of allele size at amicrosatellite locus. The occasional substitution of advantageous alleles(genetic hitchhiking) will also reduce the variance, but a high mutationrate at a microsatellite locus can restore the variance relatively rapidly.Overdominance at the selected locus will increase the variance at themicrosatellite locus and create partitioning of the variation in allelesize among gametes carrying one or the other of the overdominant alleles.These results suggest that neutral microsatellite loci can provideindicators of selective processes at closely linked loci.