Evolution of Microsatellites

Abstract

Microsatellites are tandem repeats of short nucleotide sequence (1–6 bp) and abundant in the eukaryotic genome. Mutation rate is high (10−2–10−6 per locus per generation), and there is large variation among species. Mutational changes of microsatellites are mostly repeat number change by one. However, there are some multistep changes, and the mutation rate shows a complex relationship with repeat length, repeat unit size and motif composition. Microsatellites are useful to study the evolutionary relationship among populations. Genetic distance, a measure of the extent of genetic differentiation between populations, calculated for human populations appears to increase approximately linearly with the time after population divergence. Interestingly, the total number of repeats of microsatellite loci in an individual's genome also appears to diverge with the time after population divergence. Variation of repeat number in microsatellite loci contributes the variation of genome size of an individual due to its abundance in the genome.

Key Concepts:

  • Microsatellites are tandem repeats of short nucleotide sequence (1 – 6 bp) and abundant in eukaryotic genome.

  • The mutational changes of microsatellites are mostly increase or decrease of the repeat number by one.

  • The repeat number change of microsatellite occurs through a mechanism called replication slippage.

  • The mutational pattern of microsatellites roughly follows the stepwise mutation model.

  • The equilibrium distribution of repeat number in miscrosatellites may be obtained by balance between replication slippage and disruption of repeats by point mutation as well as by balance between higher expansion rate over contraction rate for short repeats and higher contraction rate over expansion rate for longer repeats.

  • The mutation rate of microsatellites varies with size and motif of repeat unit.

  • The mutation rate and repeat length of microsatellites vary among species.

  • Genetic distance of microsatellites increases proportionally with the time after human population divergence.

  • The average difference of total repeat number of individuals between populations increases with time after population divergence.

  • Contribution of the repeat number variation of microsatellites to genome size variation may be quite large.

Keywords: mutational mechanism; mutational model; genetic distance; stepwise mutation model; population divergence; repeat number variation; genome size; human population

Figure 1.

Schematic illustration of replication slippage. (a) Normal replication. (b) Increase of repeat number. (c) Decrease of repeat number. During replication, misalignment of the template strand and the daughter strand results in the change of repeat number. If the bubble‐like structure is made in the daughter strand (b), the mismatch repair occurs in the misaligned region, and it results in increase of the repeat number. If the bubble‐like structure is made in the template strand, it results in decrease of the repeat number.

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Further Reading

DeSalle R and Amato G (2004) The expansion of conservation genetics. Nature Reviews. Genetics 5: 702–712.

Goldstein DB and Schlötterer C (1999) Microsatellite: evolution and applications. Oxford: Oxford University Press.

Schlötterer C (2004) The evolution of molecular markers – just a matter of fashion? Nature Reviews. Genetics 5: 63–69.

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Takezaki, Naoko(Oct 2010) Evolution of Microsatellites. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0022866]