Relationships between the proportions of regulatory signals in introns and the numbers exons. Analysis similar to that in Figure 4 is performed but for various regulatory chromatin marks in the introns. Gene groups represented in X-axis are the same as for Figure 4, while the proportions of regulatory marks are used in Y-axis. The figure shows that the proportions of active regulatory chromatin marks in first introns produced the same ascending trend with increasing numbers of exons in genes, and the ascending trend almost disappears from second intron onward, similar to the trend seen for conservation. NA stands for “Not-Assigned” and essentially means that the median values of signals in were 0 and therefore regression could not be performed.