FIGURE 1.

Origins and divergence of Drosophila microRNAs. (A) Tree shows taxa of the animals in which homologs of the Drosophila microRNAs were searched. MicroRNAs were assigned an evolutionary age depending on the most distant species in which a member of the same family was identified. The number of microRNAs that emerged on each branch is shown. (B) Numbers of substitutions per site between D. melanogaster and D. virilis orthologous microRNAs of different evolutionary origins, in the whole hairpin, the mature sequence, the seed sequence, and the stem extension and loop region (outside mature). X-axis labels indicate the age of each microRNA, as in A.