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Microsatellites are highly mutable nucleotide arrays composed of short motifs repeated in tandem. They are ubiquitously distributed in bacterial and eukaryotic genomes and their abundance and mutability has made them a widely used genetic marker for a variety of applications. One aim of the study of microsatellite evolution is to predict their mutational patterns in order to make them more accurate markers of genetic distance between species or individuals. Applications that use microsatellites as markers work under the basic assumption that microsatellite mutations are simple and random. However, this assumption contrasts with the observed variability of mutation rates across microsatellite loci. Several factors such as array size and sequence motif have been shown to influence microsatellite mutation rates, but research into their evolution is also complicated by the fact that some microsatellites function to regulate gene expression and possibly other genomic functions, and may therefore be subject to selective pressure. Key Concepts: Microsatellites are arrays of tandemly repeated 1–6 bp sequence motifs. They are highly abundant in all organisms studied, and they are also highly polymorphic as a result of frequent change of length mutations. The traditional view of microsatellites as neutrally evolving junk DNA is overly simplistic, which sometimes affects the accuracy of studies that use them as genetic markers. Many complex processes interact to govern the frequency with which microsatellites mutate, including array length, sequence motif and flanking sequence. Increasing evidence indicates that a subset of microsatellites function to regulate gene expression, and perhaps also interchromosomal recombination, and the evolution of these microsatellites is therefore influenced by selection. The mutability of microsatellites, the fact that their mutations are easily reversible, and their abundance and conservation in regulatory regions suggest that they may make a significant contribution to the diversity and adaptation of species, but much work remains to establish the extent of their functional importance. Keywords: tandem repeats; strand slippage; DNA ; microsatellite; polymorphism; mutation model; selection; gene; expression; strand slippage; repetitive |
