Mr. r has beta-thalassemia minor; he is heterozygous for the beta-thalassemia gene, so he only makes half as many beta chains as normal. the red blood cells containing abnormal hemoglobin are destroyed more rapidly, so mr. r suffers from mild anemia (low hematocrit). what are the beta chains, and why are they important in the hemoglobin molecule?

Hemoglobin is the molecule that transfers oxygen through the cardiovascular system. In most mammals, hemoglobin consists of 4 distinct subunits. These subunits consist of an aminoacid chain (aminoacids are the building blocks of proteins) and a heme group (heme groups are ringlike molecules with an iron ion in the middle). 2 of the subunits have a protein chain with a-structure and 2  have a protein chain with beta structure. There are alleles that are responsible for the production of both kinds of chains and if there is a mutation in one, hemoglobin chains of that kind will have a different aminoacid order and thus they will fold differently in space. Thus, they will not be able to form the compound hemoglobin molecule (the 4 subunits won't "fit"), leading to symptoms of thalassemia. Stated shortly, beta chains are a protein chain that is critical to the hemoglobin molecule because every molecule needs 2 such chains that are foldable in a specific way. If this does not happen, the beta chains cannot be utilized for hemoglobin molecules and thus the organism will have trouble with oxygen transfer in its tissues.