In with the Old, in with the New: The Promiscuity of the Duplication Process Engenders Diverse Pathways for Novel Gene Creation

Figure 4

Schematic outlining how structurally heterogeneous duplicates can neofunctionalize by escaping gene conversion based on the fog-2/ftr-1 case in C. elegans [113, 124, 185]. Consider an ancestral gene (Copy A) comprising four exons (top panel) that is partially duplicated. Small shaded rectangles represent exons. The duplication event is initiated in the 5′ flanking region and terminates within exon 4. The large transparent blue rectangle highlights the region of homology between the paralogs as do like coloured exons and introns. The derived copy B additionally recruits noncoding sequence from its genomic neighbourhood to fashion a novel partial exon 4, intron 4 and exon 5 that bears no sequence homology to ancestral copy A (depicted by orange rectangles and highlighted by a large transparent cream rectangle). This novel recruited region also imparts a novel function to copy B. The two paralogs diverge by gradual accumulation of mutations (horizontal narrow lines within exons delineate point mutations). Recurrent episodes of gene conversion of copy B (recipient) by copy A (donor) constrains sequence divergence across the region of homology. Despite high gene conversion pressure, copy B is able to preserve its neofunctionalized state due to the presence of nonhomologous coding sequence that remains unconstrained by gene conversion.