Microsatellite mutations were studied in a set of 175 mutation accumulation lines, all of them
independently derived from a completely homozygous population of Drosophila melanogaster and
maintained under strong inbreeding during 80 generations. We assayed 28 microsatellites and
detected two mutations. One mutation consisted of a single addition of a dinucleotide repeat and
the other was a deletion of five trinucleotide repeats. The average mutation rate was 5·1 × 10−6, in
full agreement with previous estimates from two different sets of mutation accumulation lines.