Frequency spectra in coding (C) and non-coding (NC) regions across species at each gene.

aFrequency spectra classes including invariant positions (f = 0), low polymorphism represented by singletons (f = 1), moderately polymorphic positions with the rare nucleotide observed twice or three times (f = 2–3), and highly polymorphic positions with the rare nucleotide observed four or more times (f = 4–7). The relative distribution of each class is expressed as percentages. Excess and deficit of observed vs. expected frequency is marked by red and blue respectively in cells with significant deviations based on 1 df χ2 test (*, **, ***, represent P<0.05, 0.01, and 0.001, respectively). The western Kenya population of A. gambiae represents this species (heterogeneity χ2 test showed no evidence for heterogeneity among the four populations). All contingency tables for each gene and species were significant (P<0.01).