Removal of microsatellite interruptions by DNA replication slippage: phylogenetic evidence from Drosophila

Microsatellites are tandem repetitions of short (1-6 bp) motifs. It is widely assumed that microsatellites degenerate through the accumulation of base substitutions in the repeat array. Using a phylogenetic framework, we studied the evolutionary dynamics of interruptions in three Drosophila microsatellite loci. For all three loci, we show that the interruptions in a microsatellite can be lost, resulting in a longer uninterrupted microsatellite stretch. These results indicate that mutations in the microsatellite array do not necessarily lead to decay but may represent only a transition state during the evolution of a microsatellite. Most likely, this purification of interrupted microsatellites is caused by DNA replication slippage.