Figure 3.

Relative levels of species-specific fixation of variant SNP alleles in each gene are correlated with the level of intrinsically disordered region content in the corresponding proteins. (a, b) Scatter plot showing the fixation index (FI) for genes, calculated by the McDonald-Kreitman test (see Materials and methods), is positively correlated with the fraction of IDR (a) and negatively correlated with the fraction of regular secondary structure (b) in the corresponding proteins. Spearman's rank correlation coefficients (r_S) and associated P-values are shown. (c, d) The (G+C) content of genes is not correlated with their FI (c) or with the fraction of IDR in the corresponding proteins (d). Spearman's rank correlation coefficients (r_S) and associated P-values are shown. (e) The mean FI corresponding to all IDRs studied is higher than that for all α-helical regions or β-sheet regions studied. The FI for concatenated tracts of predicted α-helical (α), β-sheet (β) and IDRs are plotted. Values are shown for IDR predictions using confidence thresholds of 0.8 (strict) or 0.5 (liberal) (see Materials and methods for details). Open bars designate results obtained for the non-filtered data set while the filled bars designate the data set after removal of outliers (see Materials and methods for details).