Expression of miRNA pairs originating from the same precursor. (A) Number of mature miRNA types generated per precursor in humans. A total of 347 known human precursors are represented in the dataset by at least one mature miRNA. Shown are the proportions of miRNA precursors annotated to generate two mature miRNAs (red), annotated to generate one mature miRNA, but generating two in our dataset (yellow), annotated to generate one and generating one mature miRNA in our dataset (blue). (B) Number of mature miRNA types generated per precursor in fruit fly. The total number of precursors shown is 147 and the colour code is the same as for human precursors. (C) Human miRNA precursors sorted according to the expression ratio between high- and low-expressed miRNA strands originating from the same precursor duplex. The colours represent miRNA pairs annotated as miRNA/miRNA* (orange, N = 140), as miRNA 5p/3p (red, N = 65), and the novel miRNA pairs (yellow, N = 48) discovered in our dataset.