Figure 2.

Stylized phylogenetic tree showing the relationship between human GRAFS. The number of human representatives identified within each superfamily is indicated within brackets (Fredriksson et al., 2003). Rhodopsin family members (which are represented by the blue branch) are the most numerous and their members are classified into four main sub-branches (α, β, γ, and δ). Human receptors, which are activated by peptides and have a role in feeding regulation, are members of the rhodopsin and secretin families.