Frequency variation of repeat-number allelic variation at a microsatellite locus

    The modal repeat number in this population is 9. Alternative alleles are produced by slipped-mismatch replication, which creates new alleles that differ by a single repeat unit from the parent. Models of population variation often assume that each allelic repeat class has arisen only once, for example that the 8- and 10-fold repeats originated rom the 9-fold repeat, and are thus separated by two mutations events. However, since slipped-mismatch can cause either loss or gain of a repeat unit, the same allele may be generated more than once. For example, a 9 allele may gain a repeat to produce a 10 allele, and subsequently lose a repeat so as to appear identical to the ancestral 9 allele, even though it differs by two mutations.

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Figure ©2012 TA Brown, Introduction to Genetics (1st ed.); additional text ©2014 by Steven M. Carr