Relative tissue-specificity of conserved and non-conserved polyadenylation sites. (A) Distribution of 10,000 control correlation coefficients each computed from 1000 random pairs of non-conserved sites from orthologous human and mouse genes. Arrow indicates the correlation coefficient observed for pairs of conserved sites (r = 0.10). (B) Distribution of relative tissue-specificities in conserved and non-conserved polyadenylation sites. Number of sites in human (white) and mouse (black) is plotted against relative tissue specificity.