 Notably, many teleost fish encode two distinct IFN-γ species (called IFN-γ1 and IFN-γ2) that appear to bind genetically and physically distinct IFN-γR1 chains.In all investigated tetrapods, there is a single IFN-γ gene that binds a unique IFN-γR1 chain and (in amniotes) a unique IFN-γR2 chain.Frogs appear to encode two distinct IFN-γR2 genes whose intracellular domains differ significantly.