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. 2010 Aug 19;6(8):e1001064. doi: 10.1371/journal.pgen.1001064

Figure 9. A model for the evolution of iGluRs and IRs.

Figure 9

Schematic phylogenetic tree highlighting the branches along which specific gene families or genes appeared with their putative functions, inferred from their presence or absence in sequenced genomes of extant species (see Figure 1). Solute binding proteins (SBPs, which exhibit the same protein fold as the iGluR/IR amino terminal domain and ligand-binding domain) and ion channels were likely present in primitive life forms as related protein domains exist in Eukaryota, Bacteria and Archaea [94]. iGluRs are shown in purple, IRs in red and insect GRs and ORs in green. Various speculative models for the origins of iGluRs are shown. Putative genetic ancestors from which IRs, GRs and ORs derived are shown in grey followed by a “>” symbol. The resolution of the phylogeny is necessarily biased towards invertebrate lineages and branch lengths contain no temporal information.