Neighbour-joining phylogenetic analysis of the relationship between marsupial class I genes. Bootstrap support for branches is provided. Estimated divergence times are indicated adjacent to the relevant node. The tammar wallaby class I sequences Maeu-I*01 and Maeu-I*02 are cDNA transcripts from Genbank. The phylogenetic tree is divided into the following clades; clade 1 includes MHC un-linked wallaby class I genes and expressed class I transcripts from Australian marsupials, clade 2 includes opossum class I genes only, including opossum class Ia (Modo-UA, UB and UC), clade 3 includes marsupial specific class I genes from both the American and Australian lineages.