Relative distance to enhancers (a) and promoters (b) for different transcript classes. The means and error bars depict the relative distance (D
) to the enhancer (a) and promoter (b) elements for genes in each category in these two ectodermally derived cell types (HMEC and NHEK). D
is the closest distance to the enhancer (or promoter) in NHEK (or HMEC), and D
is the average closest distance to the enhancer (or promoter) to the other cell types.