Gene expression heat maps. Heat maps of gene expression (color scale) as a function of bivalent (y-axis) and monovalent (x-axis) enrichment amplitudes for (A) H3K27me2-H3K36me3 versus H3K27me3 and (B) H3K36me3-H4R3me2 versus H4R3me2. The y-axis represents the product of the amplitudes of both marks and the x-axis represents one component of the pair. Gene expression values were binned into a 10,000 square grid with level represented by color. Vertical lines represent a constant value of the x-axis mark amplitude (i.e., H3K27me2 in (A) and H4R3me2 in (B)), while a line emanating from the origin represents a constant value of H3K36me3 in (A) and (B) with the slope corresponding to H3K36me3 level. Plot (A) shows mark avoidance, as there are few genes with high levels of both marks while (B) shows a trend toward mark concurrence. These plots also demonstrate how H3K36me3 strongly overrides H4R3me2 (increasing radial slope corresponds to increasing gene expression in (B)) but has more difficulty overriding the repressive activity of H3K27me2.