Correlation between regulatory signals and conservation in first introns. Kendall’s tau correlation analysis is performed to test how the conservation in first introns is related to density of regulatory marks. For smoothing, introns are binned into groups of 10 genes by conservation and average regulatory signal density is calculated for each bin, and plotted against the average conservation of the group. As in Figure 2, all marks are obtained from GM12878 cell line, and the results from the other two cell lines are provided in Additional file 1: Figure S3A, B. Kendall’s tau values and p-values are shown; significant p-values (p < 0.05) are represented by bold font. All active chromatin marks show significant positive correlations between conservation and the proportions of the regulatory marks.