Human haplo-insufficient genes tend to bear the most highly conserved miRNA binding sites. (A) Known haplo-insufficient genes in humans (Dang et al. 2008) exhibit more conserved miRNA binding sites than other human genes. (B) Conservation of miRNA binding sites correlates with the probability of human genes for being haplo-insufficient, as calculated by Huang et al. (2010) (genes were binned into boxplots according to their P_CT for clarity). In every boxplot in this figure, the number of genes in each category is indicated inside the boxes. Note: Even though the P_CT was initially defined as a probability (Friedman et al. 2009), values in the latest P_CT data set (in TargetScan v7, described in Agarwal et al. [2015]) can be larger than 1.