Fig. 3

Genes from different GO categories show different codon frequencies. a–c Codon frequencies were calculated per Gene Ontology (GO) term, and PCA was used to reveal a global separation into high and low GC genes (a). GO terms are coloured according to total GC (a), GC at the third codon position (b), or at the first and second position (c). Examples of GO terms are listed next to the graphs. d PCA loadings plot identifying the codons contributing the location of the GOs in a–c. Codons are colour coded by third position base and/or codon degeneracy. The separation across the x-axis is comparable to the separation across the diagonal in Fig. 2a, b, d, e