Phylogenetic tree based on the nucleotide sequences of representative OR genes located on chromosome 4.Family 262 is segregated on three different branches (1-3).Their cluster affiliation is indicated by shading: black, `mOR37' cluster I; medium gray, `mOR37' cluster II; light gray, single gene at position 57.7 Mb. The mouse melanocyte-stimulating hormone receptor (mMSH-R) was used as an outgroup.Pseudogenes are marked with an asterisk.Because the gene mOR37A was not given a new name in the study by Zhang and Firestein (2002), we named it mOR262-14.