An orphaned mammalian beta-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 th ought to be derived from a single ancestral gene, by duplication events tha t occurred after the separation of the mammals and birds. We report the iso lation and characterization of an atypical beta -like globin gene (omega -g lobin) in marsupials that appears to be more closely related to avian beta -globin genes than to other mammalian beta -globin genes, including those p reviously identified in marsupials. Phylogenetic analyses indicate that ome ga -globin evolved from an ancient gene duplication event that occurred bef ore the divergence of mammals and birds. Furthermore, we show that w-globin is unlinked to the previously characterized beta -globin gene cluster of m arsupials, making this the first report of an orphaned beta -like globin ge ne expressed in a vertebrate.