Distributions of TpG and CpA scores in 1-kb promoters. The left histograms show the distributions of TpG scores in the ascidian (A), human CpG-poor (B), and CpG island promoters (C). The right histograms show the distributions of CpA scores in the ascidian (D), human CpG-poor (E), and CpG island promoters (F). Vertical dotted lines indicate the positions of mean, i.e. 1.14, 1.24, 1.00, 1.14, 1.24, and 0.99 for (A)-(F), respectively The score 1.0 means that the observed and expected numbers of the dinucleotide are equal, suggesting no methylation effect in this case.