Background: The developing fetus has a different kind of hemoglobin than most normal adults. Fetal hemoglobin (hemoglobin F) consists of two ? chains and two ? chains, whereas adult hemoglobin (hemoglobin A) consists of two ? chains and two ? chains. Fetal hemoglobin is synthesized beginning at the third month of gestation and continues up through birth. After birth, hemoglobin F synthesis declines and synthesis of hemoglobin A increases (synthesis of the ? chain declines, and synthesis of the ? chain increases). By the time the baby is six months old, 98% of its hemoglobin is hemoglobin A.

Question: The chain differs slightly in structure from the chain and has fewer Lys and His residues than the chain. This means that hemoglobin F has fewer positive charges in its central cavity than does hemoglobin A. Given this information, explain why hemoglobin F has a higher affinity for oxygen than does hemoglobin A.