Phylogenetic tree of the olfactory receptor gene family. This phylogenetic tree was constructed employing the neighbor-joining method (Saitou and Nei 1987). Sequences were derived from the conserved region between transmembrane segments 2 and 7 in 156 olfactory receptor genes (five “defective type,”, 11 “expressed gene or gene candidate type” OR genes in 1q21–q22 and 140 human olfactory receptor genes submitted to GenBank). Five major families classified by this phylogenetic tree were designated G1, G2A, G2B, G3A, and G3B according to Rouquier et al. (1998). Blue and yellow boxes indicate the olfactory receptor genes located on 1q21–q22 and 6p21.3, respectively. Purple and orange boxes indicate olfactory receptor genes located on chromosomes 1 and 6, respectively, but within unknown subchromosomal locations.
