Phylogenetic tree of the TRAV, TRDV and TRA/DV gene segments from mammalian and avian species using the neighbor joining method. Opossum TRV sequences are indicated in bold. Mammalian gene segments that are known to be expressed as TRA/DV are indicated with an asterisk. TRV genes fall into eight groups (A-H, indicated with braces) which indicate the evolutionary relationship of these genes. Branch supports are indicated as the percentage of trees based on 1000 bootstrap replicates.