A portion of sequences for two types of hemoglobin are shown in the diagram.
The top sequence for wild-type hemoglobin is C-C-T, G-A-G, G-A-G. The bottom sequence for sickle-cell hemoglobin is C-C-T, G-T-G, G-A-G.
Sickle-cell anemia is caused by a mutation of one nucleotide in a gene. Using the diagram, which type of mutation is responsible for sickle-cell anemia?
A. a frameshift mutation
B. an insertion mutation
C. an inversion mutation
D. a substitution mutation
choose the correct answer