(A) Number of species with at least one tRNA switching event in each domain of life. (B) The anticodon UUC convergently evolved in Mus musculus. A maximum likelihood phylogeny of tRNA sequences in M. musculus that decode glutamic acid (Glu) codons. Branch lengths express average nucleotide substitutions per site. Decimals on internal branches express branch support. (C) A comparison of nucleotide sequences for glutamic acid tRNA genes in M. musculus with anticodon UUC (top, tRNA1547 and tRNA359), ‘switched’ UUC tRNAs (middle, tRNA286 and tRNA754), and CUC tRNAs (bottom, tRNA1002, tRNA745, tRNA303, tRNA999, tRNA996 tRNA709, tRNA1001, tRNA1912 and tRNA81). The anticodon triplet is boxed in gray. Red vertical bars indicate differences between sequences. (D) The anticodon UAC convergently evolved in Homo sapiens. A maximum likelihood phylogeny of tRNA sequences in H. sapiens encoding for valine (Val) is shown. (E) A comparison of nucleotide sequences for H. sapiens tRNAs with anticodons UAC (top, tRNA6), a ‘switched’ UAC tRNA (middle, tRNA40), and an AAC tRNA (bottom, tRNA136). The number of genes is according to the tRNA database.