An orphaned mammalian β-globin gene of ancient evolutionary origin

Mammals possess multiple, closely linked beta -globin genes that differ in the timing of their expression during development. These genes have been thought to be derived from a single ancestral gene, by duplication events that occurred after the separation of the mammals and birds. We report the isolation and characterization of an atypical beta -like globin gene (omega -globin) in marsupials that appears to be more closely related to avian beta -globin genes than to other mammalian beta -globin genes, including those previously identified in marsupials. Phylogenetic analyses indicate that omega -globin evolved from an ancient gene duplication event that occurred before the divergence of mammals and birds. Furthermore, we show that w-globin is unlinked to the previously characterized beta -globin gene cluster of marsupials, making this the first report of an orphaned beta -like globin gene expressed in a vertebrate.