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. Author manuscript; available in PMC: 2009 Jun 11.
Published in final edited form as: Trends Ecol Evol. 2008 Aug 18;23(10):578–587. doi: 10.1016/j.tree.2008.06.005

Figure 2.

Figure 2

Genesis and evolution of miRNA loci. a) Inverted duplication model of the origin of plant miRNAs [45] and potential pathways of stabilization of new miRNA loci in plants [4]. A new miRNA is selected with the capacity to regulate the progenitor or a family member gene (1), or unrelated gene (2). b). Origin of miRNAs from genomic repeats or transposable elements in animals [48-52]. c) Random selection model of miRNA origin [53]. Potential miRNA genes are selected from hairpins encoded in the genome. Random targeting of transcripts by potential miRNAs could be deleterious with only a few targets being selectively neutral or advantageous. Acquisition and expression of a potential novel miRNA gene can occur only when, by chance, it is not strongly deleterious [41].