Fig. 1

Internal correspondence analysis of single-exon genes and multiple-exon genes in rice. The total codon usage variability is decomposed into the synonymous codon usage (within-AA) variability (a, d, g), amino acid usage (between-AA) variability (b, e, h), and variability of within (a, b, c) and between gene types (d, e, f). The performance of ICA yields nine elementary analyses (a–i). In each peculiar analysis, the contribution to the total codon usage variation is indicated, where only the first 10 eigenvalues are represented for comparison