The sequences of the template strands are indicated by the middle line, with the microsatellite sequence in red. Arrow indicates direction of DNA synthesis (5’ to 3’ direction). (A). Error specificity within complementary [G]10 and [C]10-R alleles. (B). Error specificity within [G]9 and [C]10 alleles inserted in the same sequence context as the [G]10 allele. Open triangles, single base insertion; open diamond, two base deletion; closed triangles, single base deletion; closed diamond, two base deletion. N, number of independent microsatellite errors observed. See Table S1 for mutation frequencies.