This indicates that template stability may affect the mutation rate, perhaps by reducing the frequency of strand-slippage events. Finally, a comparison of human, chimpanzee, gorilla, orang-utan, baboon, and macaque microsatellite repeat length has shown that humans have significantly longer loci than those found in the other primates. Rubinstein et al. The consequence of the observed selection on repeat length is that the number of homoplasies should increase over that predicted by the SMM, as the mean size of the microsatellite alleles increase. Estoup et al.
Irregular repeats are core repeats that are interrupted by point mutations.
The presence of these mutations allows alleles with similar sizes to be distinguished. In this survey the majority of loci examined were not simple repeats but composites made up of 2 or 3 core repeat units. These studies are of interest because they suggest that the more complex the repeat structure, irregular or composite, the lower the likelihood of single step mutational events.