Date of divergence of the CTG codon reassignment using Ser-tRNA_CAG sequences. (A) Nonlinearized tree; (B) linearized tree. The tree was constructed using the NJ method and the Kimura 2-parameter distance model (Kimura 1980). A γ shape parameter of 1.83 was used. A nucleotide substitution rate of 1.156 × 10⁻⁹ substitutions per site per year was used to estimate divergence dates. This value was calculated to be representative of yeast tRNAs, as described in Methods. The standard error of the key divergence time is indicated. Lower numerals represent the confidence level from 100 replicate bootstrap samples. Homo sapiens Ser-tRNA_GCT (HomoGCT) was used as an out-group. The scale represents the average number of substitutions per site.