Results: Functional similarity. Functional similarity of host and target gene sets as predicted by TargetScan. (A) Frequency distribution of the functional similarity score for all 75 host-target relations. For each single host gene and its set of target genes, we calculate a mean score based on the GO annotation 'biological process'. The mean functional similarity of the host gene Copz1 to its predicted targets is 2.48 (blue line). (B) Comparison of the real functional similarity score the host gene Copz1 with a null model distribution. For the null model, a random set of miRNA target genes of the same size has been chosen 1000 times and the functional similarity score has been calculated. The real score of Copz1 deviates significantly from the null model distribution, resulting in a high Z-score. (C) Z-scores for all annotated host genes. A total of 21 out of 75 host genes show Z-scores > 2 and thus display a significantly higher functional similarity as expected from a random sample of target genes.