Features of the identified novel human miRNAs. (a) Inferred evolutionary origin of known and novel human miRNAs. Representative species are shown for each clade: hominids are represented by chimp; old world monkey, baboon; primate, tarsier; simian, tree shrew; placental mammal, armadillo; mammal, platypus; tetrapod, clawed frog; and vertebrate, zebrafish. The miRNAs have been divided into those specific to hominids and humans (‘specific’ in light green or orange) and those conserved in old world monkeys or beyond (‘conserved’ in dark green or brown). (b,c) Genomic sources of known and novel miRNAs. (d) Specificity of expression. The horizontal axis shows the number of datasets (out of 94) in which the miRNA is detected. The vertical axis shows the cumulative fraction of miRNAs present in at least these many datasets. The horizontal blue line indicates the median number of datasets in which the miRNAs are present. Examples of miRNAs detected in all 94 datasets are noted. (e) Maximal expression. As in the previous figure, except the maximum expression of each miRNA in any of the 94 datasets is shown. Expression is normalized (transcripts per million reads) to adjust for varying sequencing depth between the samples. The miRNA with the highest normalized expression in any dataset is let-7 f. (f-i) The processing precision of known and novel miRNAs. The precision is defined as the fraction of mapping reads that correspond to the consensus end position of the sequence. The miRNAs are sorted on the x-axis such that the most precisely processed one is at percentile 1 and the least precisely processed one at percentile 100. Dark colors indicate conserved miRNAs, light colors non-conserved.