Number of peaks and peak-containing promoters for each cell type and epigenetic mark. A. Number of peaks found per epigenetic mark per cell type. This analysis used generous parameters leading to relatively large numbers of potential peaks. B. Number of promoters possessing each epigenetic mark. Peaks were mapped to proximal promoter regions; if a peak (or multiple peaks) overlaps a promoter, the promoter was scored as positive (see RESULTS and METHODS for details). Note large differences among cell types in number of H3K9me3+ promoters.