the CpG density within each promoter category (Fig. 2C), we observed that DNA methylation levels of the three promoter categories were markedly different during early embryo development (at neurulation stage) chi-square p-value <2.2 × 10−16 against the CpG density (Fig. 2C). The ratio of hypermethylated genes in each category (see dots above the dash line in Fig. 2C) were sharply different, with 3% (of 11,071 genes) in HCP, and 10% (of 4,363 genes) in LCP, compared to 31.5% (of 2,908 genes) in the ICP groups.
