Modeling evolutionary growth of a microRNA-mediated regulation system

► We introduce a model for the evolutionary growth of a miRNA gene regulation system. ► We focus on the role of gene duplication in the evolution of complexity. ► The model flexibly incorporates the positive and negative effects of gene duplication. ► The model is applied to Arabidopsis thaliana miRNAs. ► The growth of Arabidopsis mRNA systems should involve bidirectional evolutionary forces.