Evolution and molecular characterization of a beta-globin gene from the Australian echidna Tachyglossus aculeatus (Monotremata)

Coinciding with a period in evolution when monotremes, marsupials, and euth erians diverged from a common ancestor, a proto-beta-globin gene duplicated , producing the progenitors of mammalian embryonic and adult beta-like glob in genes. To determine whether monotremes contain orthologues of these gene s and to further investigate the evolutionary relationships of monotremes, marsupials, and eutherians, we have determined the complete DNA sequence of an echidna (Tachyglossus aculeatus) beta-like globin gene. Conceptual tran slation of the gene and sequence comparisons with eutherian and marsupial b eta-like globin genes and echidna adult beta-globin indicate that the gene is adult expressed, Phylogenetic analyses do not clearly resolve the branch ing pattern of mammalian beta-like globin gene lineages and it is therefore uncertain whether monotremes have orthologues of the embryonic beta-like g lobin genes of marsupials and eutherians, Four models are proposed that pro vide a framework for interpreting further studies on the evolution of beta- like globin genes in the context of the evolution of monotremes, marsupials , and eutherians. (C) 1999 Academic Press.