Figure 6

Evolution of family 2 GPCRs in the metazoa. Diagram illustrating the increase in gene number and gene structure complexity of the TM domains regions of family 2 GPCR receptor genes in protostomes (nematodes and arthropods) and deuterostomes (tunicate and vertebrate). The proposed species-specific gene duplications are indicated in the figure. Putative gene or genome duplication events of ancestral family 2 GPCRs during metazoan evolution are indicated by arrows (dashed arrow – represent several duplication events within the chordate lineage). The number of receptors identified in each species is within brackets. Exons are represented by blocks and introns by lines and the molecular evolutionary time for each species is indicated in MYA (million years ago) and was obtained from Hedges and Kumar, 2003 [82] and (*) from Dehal et al. 2002 [42]. The TM domain regions are represented by shaded regions and numbered. Intron/exon boundary phases are indicated below each exon. The tunicate and vertebrates family 2 GPCR members have been grouped according to their common gene organisation. The figure is not drawn to scale.