Nonsense suppressors: two mutations, nonsense mutation in mrna; trna anticodon mutated, recognizes stop codon, advantages, able to recover nonsense mutation that would normally result in truncated, two mutations work together to conserve making of polypeptide chain. Normal hemoglobin found in adults called adult hemoglobin consists of two a and two b polypeptide chains. Sickle cell hemoglobin, which causes sickle cell anemia, arises from a mutation in the b 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, indicate the type (transition or transversion) and location in the codon of the mutation that gave rise to sickle-cell anemia. Spontaneous: naturally occurring mutations. e. g. replication, cell growth and division, depurination, deamination.