Hemoglobins in Sheep: Multiple Differences in Amino Acid Sequences of Three Beta-Chains and Possible Origins

Among the three adult sheep hemoglobins (A, B, and C), two (A and B) are reportedly products of alleles. The β-chains of A and B differ by at least seven scattered amino acid residues whereas the β-sequence of C differs from A by at least 16 residues and from B by at least 21 residues. These changes suggest that the origin of C-β antedated the divergence of A and B. Five shared differences between A-β and C-β with respect to B-β can be interpreted as the result of selective advantage in favor of B. A complex of additional mechanisms has possibly been involved in maintaining the A-B- C porymorphism.