Figure 4

Evolutionary models used in the ML analysis. Scheme of the evolutionary models compared in the codon model substitution-based ML analysis. ω₀, ω₁, ω₃ and ω₃ denote different d_N/d_S ratios. Model 1 (null model), Model 2 (alternative model 1) and Model 3 (alternative model 2) have 44, 45 and 46 free parameters (the degrees of freedom for each LRT is equal to the difference in the number of free parameters), respectively.