Hemoglobin theta-1 may be expressed very early in embryonic life, perhaps sometime before 5 weeks. Theta-1 is a member of the human alpha-globin gene cluster that involves five functional genes and two pseudogenes. The order of genes is: 5' - zeta - pseudozeta - mu - pseudoalpha-2 -pseudoalpha-1 - alpha-2 - alpha-1 - theta-1 - 3'. Research supports a transcriptionally active role for the gene and a functional role for the peptide in specific cells, possibly those of early erythroid tissue.The orangutan gene, called theta-1, has all the sequence elements necessary for an expressible, protein-coding gene although its actual expression and function are unknown. Theta-1 in the orangutan is located 3 kb downstream from the adult alpha-1 gene. The putative polypeptide for which it codes is 141 amino acids long, identical to the alpha and zeta globins.