Results of maximum-likelihood models for exon 2 of the DRB gene in the baiji.

Analyses were completed using CodeML (included in the PAML 4 program suite). An alignment of 9 DRB sequences (213 bp) from the baiji was used as the input for CodeML. P is the number of parameters in the ω distribution, ω is the selection parameter (dN/dS), K estimated transition/transversion rate ratio, and pn proportion of sites that fall into the ωn site class. For models M7 and M8, p and q are the shape parameters of the β function. Positively selected sites were identified in models M2a and M8 by the Bayes empirical Bayes procedure [57]. Sites inferred to be under positive selection are given at the 80% confidence interval level and the levels are given in parentheses. See “Data analysis” and Yang et al. [58] for detailed method description.