Hemoglobin is a complex protein that contains four polypeptide chains. the normal hemoglobin found in adults, called adult hemoglobin, consists of two alpha and two beta polypeptide chains, which are encoded by different loci. sickle cell hemoglobin, which causes sickle cell anemia, arises from a single mutation in the beta chain of adult hemoglobin. adult hemoglobin and sickle cell hemoglobin differ in a single amino acid. the sixth amino acid from one end in adult hemoglobin is glutamic acid, whereas sickle cell hemoglobin has valine at this position. After consulting the genetic code provided in Figure 15.10, indicate the type and location of the mutation that gave rise to sickle-cell anemia.