Contraction and expansion of polymorphic short tandem repeats (STRs). (A) The distribution of base-pair differences for polymorphic STR alleles compared with the reference alleles is shown. Positive and negative values on the x-axis indicate allele expansion and contraction, respectively, compared with the reference alleles. (B) The distribution of contraction (in yellow) and expansion (in blue) scores for each pSTR. Expansion score = [max(STR length) – median(STR length)]/median(STR length); contraction score = [min(STR length) – median(STR length)]/median(STR length). (C) Comparison of the log10 transformed absolute values between contraction (in yellow) and expansion (in blue) scores in polymorphic STRs with different motif lengths. (D) Comparison of allele frequencies between contracted (in yellow) and expanded alleles compared with the median allele length in polymorphic STRs with different motif lengths. The mean and median values in (C,D) are indicated as red points and horizontal lines in each box, respectively (Supplemental Table S2). Statistical significance was calculated using the two-sided Wilcoxon test and was corrected for multiple comparisons (Bonferroni method). Significance of each comparison (Supplemental Table S2) is shown above each comparison pair (ns: adjusted P > 0.05, [**] adjusted P ≤ 0.01, [***] adjusted P ≤ 0.001, [****] adjusted P ≤ 0.0001). (E) Percent of alternative alleles showing contraction, expansion, and substitution in di-STRs. The total number of di-STRs with different motif sequences is indicated above each stacked bar.
