a, Average percentage of genes with zero, one or two CUG and CUA codons in Candida (grey bars) and Saccharomyces (black bars). Error bars, s.d. All differences are significant with P ≤ 0.0004 (t-test, N = 8 Candida spp. and 6 Saccharomyces spp.) except for those in genes with two CUA codons (P = 0.02). ‘Candida’ and ‘Saccharomyces’ here refer to the CTG and WGD clades in Fig. 1, but including Pichia stipitis and excluding C. dubliniensis. b, CUN codon usage for all codon counts. c, Decoding rules for CUN codons in Saccharomyces and Candida.