Question

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

Answer 1

D.

Step-by-step explanation:

Sickle-cell anemia is caused by a point mutation, specifically a single nucleotide substitution, which is the replacement of one nucleotide in the DNA sequence with another. In the diagram provided, the wild-type hemoglobin sequence is shown as C-C-T, G-A-G, G-A-G and the sickle-cell hemoglobin sequence is shown as C-C-T, G-T-G, G-A-G. The difference between these two sequences is that the wild-type has an adenine (A) at the second position of the second codon (GAG) while the sickle-cell hemoglobin has a thymine (T) at the same position. This single nucleotide change in the DNA sequence results in a change in the amino acid sequence of the hemoglobin protein, and this is what causes the abnormal sickle-shaped red blood cells.