The extent of alternative isoform expression differences within population sets. (A). Spearman correlations of isoform (L) ratios between individuals. Correlations were computed separately for each pair of individuals, and clustered according to similarity using average linkage hierarchical clustering. Only genes with sufficient read coverage (FPKM ≥5) in all individuals were used. (B). The fractions of AS events show significant differences between at least two individuals within population sets (N1, 8 individuals from northern populations; N2, 6 individuals (excluding more divergent PT18 and PT20 samples) from northern populations; S, 12 individuals from southern populations). Variation in AS events at an adjusted Fisher’s exact P-value cutoff corresponding to a false discovery rate of 5% between at least one pair of individuals within the population set were considered significant. Only genes with sufficient read coverage (FPKM ≥5) in all individuals were used.