Frameshift mutation alters downstream protein sequence

Steps:

• Identify the mutation type from the DNA coding strand diagram: a base insertion or deletion shifts the reading frame after the GUG codon site.
• Recognize that frameshifts change all subsequent codons, leading to different amino acids.
• Confirm the Hb^S allele produces an altered β-globin due to this shift, unlike the normal Hb^A.
• Rule out point mutations, as the diagram indicates a frameshift effect.

Why A is correct:

• Frameshift mutations, by definition, alter the reading frame, causing all amino acids after the mutation site to differ due to shifted codon boundaries.

Why the others are wrong:

• B: Hb^S mRNA has GUG (not CAC) replacing GAG; CAC/CUG are unrelated codons.
• C: Hb^A mRNA retains GAG (not GAC or GTC); this misstates normal sequence.
• D: The mutation is frameshift, not nonsense; translation continues with errors.

Final answer: A