Relationships between gene expression and methylation in different genic regions and sequence contexts.(a) Promoter methylation. (b) TTR methylation. (c) Gene body methylation. Methylation was measured using absolute methylation level (total methylation level of mCs divided by sequence length of the calculated region). Genes are categorized into unmethylated (black line) and methylated ones, and the latter were further divided into five groups based on methylation level (from Group 1 of the 20% of genes with the lowest methylation to Group 5 of the 20% with the highest methylation level). Gene expression level was measured by log2 value of its tag number and is indicated on the x axis. The fraction for each group of methylated and unmethylated genes is shown on the y-axis.