Figure 5

Proposed evolutionary history of the visual opsin gene-bearing chromosome regions. The proposed evolutionary scenario also includes the oxytocin/vasopressin receptor gene family (OT/VP-R), the voltage-gated calcium channel L-type alpha subunit gene family (CACNA1-L) and the G-protein alpha transducing (GNAT) and alpha inhibiting (GNAI) gene families. This scenario is consistent with data from additional neighboring gene families (see Conserved synteny analyses in Results). Local duplications before 2R occurred in the visual opsin and OT/VP-R gene families, giving rise to ancestral SWS and LWS genes, and ancestral V1/OTR and V2 genes respectively. The chromosome region subsequently quadrupled in 2R, giving rise to paralogous genes in all gene families. For the visual opsin gene family, the ancestral SWS gene gave rise to the SWS1, SWS2, RH1 and RH2 genes. However, only one copy of the LWS gene was retained. Early in actinopterygian evolution, before the divergence of spotted gar and teleost fishes, the RH1 gene was retrotransposed, giving rise to an intron-less RH1 duplicate. In the OT/VP-R family the V1B gene was lost. Following this, the chromosome regions duplicated in 3R, giving rise to duplicates of GNAI1, GNAI2, V1A, CACNA1D, CACNA1C and likely also RH1 (rho and rhol) and CACNA1F. We propose the nomenclature V1Aa and V1Ab for the 3R-generated V1A duplicates. After 3R, local duplications of the RH2, OTR and V2A genes occurred and extensive chromosomal rearrangements moved genes between the paralogous chromosome regions. Black arrowheads mark LWS, SWS1 and RH2 genes that have lineage-specific local duplicates in some teleost species.