Figure 2.

Proposed scenario for the duplications, losses and divergences underlying the expansion of visual GRKs in jawed and agnathan vertebrates. (a) Vertical lines denote hypothesized timing of genome duplications and speciation: 1R (first) and 2R (second) rounds of whole-genome duplication; A–J, divergence of the ancestors of extant agnathan vertebrates (A) and jawed vertebrates (J). Branch marked with open square denotes tandem gene duplication; branches marked with open circles indicate genome duplications; unmarked branches denote speciation; incomplete lines indicate gene loss. Red and blue denote presumed ancestral function in photopic and scotopic photoreception, respectively. (b) Diagrammatic representation of the hypothesized block arrangement of genes at four time points: ancestral; after tandem duplication; after 1R and after 2R. In the final post-2R set, grey shading denotes isoforms retained only in agnathans, whereas white denotes isoforms retained only in jawed vertebrates.