Hemoglobin is involved in oxygen transport from the lung to the various peripheral tissues. The alpha (HBA) and beta (HBB) loci determine the structure of the 2 types of polypeptide chains in adult Hemoglobin. The normal adult Hemoglobin tetramer consists of two alpha chains and two beta chains. Mutant beta globin causes sickle cell anemia. Absence of beta chain causes beta zero thalassemia. Reduced amounts of detectable beta globin causes beta plus thalassemia.