Distribution of CpG suppression and CG content of genomes studied. Distribution of CpG suppression, measured by ρCG, against the CG content of many genomes; evolutionarily interesting groups are differentiated by symbols. Notice that the tetrapods, all of whose genomes have multimodal k-mer spectra, form a tight grouping in the lower middle part of the graph. The three closest partitions of human genomic sequence, the introns, 3' UTRs and promoter regions (5,000 bp upstream of the 5' UTR), also have multimodal k-mer spectra. Other nearby genomes, Entamoeba histolytica and Japanese medaka (Oryzias latipes), as well as other kinds of human genomic sequences (exons, 5' UTRs, and shorter promotor regions) have unimodal spectra.