Hemoglobin binds oxygen in the lungs and releases it when the red cells reach peripheral tissues, such as the liver. The binding and release of oxygen by hemoglobin is essential for survival. Each hemoglobin molecule contains four subunit proteins. Two of the subunit proteins are called alpha and two are called beta. Hemoglobin properly binds and releases oxygen only when two alpha subunits are connected to two beta subunits.
All cells contain pairs of idential chromosomes, one from the father and one from the mother.
Each chromosome contains thousands of genes lined up in sequence. As shown in Figure 1, each person has two beta globin genes, one from the father and one from the mother. The two beta globin genes contribute equally to the production of beta globin subunit protein. The alpha globin genes together produce an amount of alpha globin protein that exactly equals the beta globin protein. Since there are four alpha globin genes compared to two beta globin genes, each alpha globin gene produces only about half as much protein as a beta globin gene.