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

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