Nucleotide diversity of the depressant toxin family gene domains. (A) The nucleotide diversity (presented as the number of substitutions per site) of the depressant toxin family gene domains, as well as at the wobble position of the negatively-selected sites in the leader and mature-coding domain, was calculated by the Jukes and Cantor parameter model . The different gene domains are indicated. (B) Sliding window analysis of the substitution rate per site (pI values) across the depressant toxins gene family. A high substitution rate was found in the mature toxin coding region (M), as compared with the gene regions coding for the leader (L), the intron or the untranslated regions (unmarked), as indicated above. (C) The transversions to transitions (Tv/Ts) ratio in Boi genes. Tv/Ts ratio was calculated for the leader and mature regions of the depressant and α-toxin families. Tv/Ts averages and SEM values for each region are shown. For comparison, the Tv/Ts ratio of the depressant toxin family introns is presented.