Posterior means of ω across DQA , exon 2, codon sites. Posterior means of ω calculated over 11 site classes under the random-sites, codon-based model M8 (beta and omega) and Bayes empirical Bayes (BEB) approach as implemented in PAML . Error bars indicate S.E. of the mean and the asterisk (*) denotes significant positive selection with a posterior probability > 95%. The dashed red line shows where ω = 1. Predicted antigen binding sites, based on HLA equivalents , are notated by the red triangles.