Figure 3. DNA methylation profiles in the distal promoter and first intron region. (A,C) Detailed maps of CpG sites in the distal promoter and 1st intron region, respectively. The short vertical bars indicate the location of CpG sites, and the numbers below the bars show the exact location in the COL1A1 map. (B,D) The degree of methylation at each CpG site. The averages of the frequencies of methylation at each CpG site in four younger and four older humans were calculated with their standard deviations. Open columns represent younger humans, and the closed columns, older humans. The bars on each column show standard deviations. The asterisks above the bars indicate that the levels of methylation are different between younger and older tissues at a statistically significant level, p < 0.05.