HIGH MUTATION-RATE OF A LONG MICROSATELLITE ALLELE IN DROSOPHILA-MELANOGASTER PROVIDES EVIDENCE FOR ALLELE-SPECIFIC MUTATION-RATES

Within recent years, microsatellite have become one of the most powerf ul genetic markers in biology. For several mammalian species, microsat ellite mutation rates have been estimated on the order of 10(-3)-10(-5 ). A recent study, however, demonstrated mutation rates in Drosophila melanogaster of at least one order of magnitude lower than those in ma mmals. To further test this result, we examined mutation rates of diff erent microsatellite loci using a larger sample size. We screened 24 m icrosatellite loci in 119 D. melanogaster lines maintained for approxi mately 250 generations and detected 9 microsatellite mutations. The av erage mutation rate of 6.3 x 10(-6) is identical to the mutation rate from a previous study. Most interestingly, all nine mutations occurred at the same allele of one locus (DROYANETSB). This hypermutable allel e has 28 dinucleotide repeats and is among the longest microsatellite reported in D. melanogaster. The allele-specific mutation rate of 3.0 x 10(-4) per generation is within the range of mammalian mutation rate s. Future microsatellite analyses will have to account for the dramati c differences in allele-specific mutation rates.