Figure 1. Factors and processes affecting microsatellite mutation. Factors (italics) operate at different hierarchical levels (orange boxes), starting from the smallest scale the microsatellite locus itself and moving up to the species level. Selection operates across all levels. All these factors interact dynamically, affecting the rate of replication slippage and recombination and, therefore, microsatellite variability.

Figure 2. Models of tandem repeat length mutation. Unequal crossover, involving misalignment of homologous chromosomes or sister chromatids (Part A) and strand slippage (Part B) are the two main types of mechanism that have been proposed. Strand slippage can occur during any process requiring DNA synthesis, including recombination (Part C).

Figure 3. Functional implications of microsatellite length change. Microsatellite length variations have been shown to mediate diverse functions depending on the genomic region in which these are present. Within exons microsatellite mutations can induce changes in protein structure, therefore altering its function, or can directly inactivate the protein by trunctation or fusion of open reading frames (ORFs). Within introns and intergenic regions these changes can partake in the modulation of gene expression, either by modifying the structure of transcription factors or enzymes involved in transcription modulation, or by changing the secondary and/or tertiary structure of DNA or RNA regions that interact with transcription factors. Furthermore, microsatellites are involved in the regulation of their own and genome-wide mutation rates, by being present within the minor components of the mismatch repair system.