Low mutation rates of microsatellite loci in Drosophila melanogaster

Analysis of variation at microsatellite DNA loci is widely used in studies of parentage(1), linkage(2) and evolutionary history(3-5). The utility of microsatellites is primarily due to high levels of allelic diversity. believed to reflect mutation rates orders of magnitude higher than base pair substitutions at single-copy genes. For humans(6-14). mice(15-16), rats(17) and pigs(18) microsatellite mutation rates have been estimated at 10(-3)-10(-5). However. a recent study comparing microsatellite variation in humans with non-human primates suggests that microsatellite mutation rates may vary considerably across taxa(19,20). We measured mutation rates of 24 microsatellite loci in mutation accumulation lines of Drosophila melanogaster. Surprisingly, only a single mutation was detected after screening 157,680 allele-generations. yielding an estimated average mutation rate per locus of 6.3 x 10(-6), a mutation rate considerably lower than reported for various mammals. We propose that the comparatively low mutation rate is primarily a function of short microsatellite repeat lengths in the D. melanogaster genome.