Fig. 3

Codon usage distributions of all merged protein-coding genes among various pulmonate species. Color key: Color value around 1 (green region) implies that a codon was observed about 1 time in 60 codons indicating a uniform distribution. Higher (red) and lower (blue) values indicate deviations of uniform distribution (as factors). This map also helps us visualize the implicit variability in amino acid distribution. a Hierarchical clustering (average linkage method) of codon patterns (y-axis) approximately groups together the examined families. Closely related species (i.e., from the same tribe) generally have highly similar codon usage. Clustering of codon frequencies (x-axis) facilitates the visual identification of deviations. b The evaluation of relative synonymous codon usage