ML estimates of the present models with the respective selective constraints for the 1-PAM KHG-derived amino acid and KHG codon substitution matrices.

aIn all models, codon frequencies are taken to be equal to the observed ones. If the value of a parameter is parenthesized, the parameter is not variable but fixed to the value specified.b for the KHG-derived amino acid substitution probability matrix, and for the KHG codon substitution probability matrix; see text for details.dNote that these ratios are not the ratios of the rates per site but per codon; see text for details.