Gene duplication is a major source of evolutionary novelty because paralogous (duplicated) genes can acquire new functions. Paralogous genes are preserved in the genome mainly through subfunctionalization (the division of an ancestral function). The duplication-degeneration-complementation (DCC)model proposes that subfunctionalization occurs when duplicated genes retain different subsets of regulatory elements (so-called complementary degeneration). But, on , Jarinova and colleagues claim that the DDC model does not totally explain the evolution of duplicated hoxb5 genes in teleosts. In zebrafish, the expression patterns of hoxb5a and hoxb5bsuggest that the ancestral hoxb5 gene underwent subfunctionalization. By comparing the Hoxb5 loci of human, mouse, zebrafish and Takifugu, the researchers identify conserved non-coding elements(CNEs) near the zebrafish hoxb5 genes. Analysis of the regulatory activities of these CNEs individually and collectively in transgenic assays shows that multiple CNEs are needed to target reporter gene expression to specific hoxb5a and hoxb5b expression domains. Thus,complementary degeneration of regulatory elements might not be the only route to subfunctionalization.
