DNA mutation alters mRNA codon, enabling different tRNA binding for amino acid substitution Steps:

• Compare template strands: HbS differs from HbA in the triplet (GTG vs. AAG), a point mutation affecting transcription.
• Transcribe to mRNA: The HbS template produces an altered codon complementary to 3'-GTG-5' (5'-CAC-3' in mRNA).
• Analyze translation: The changed mRNA codon pairs with a specific tRNA anticodon via complementary base pairing.
• Determine protein impact: Different tRNA binding incorporates a nonstandard amino acid, yielding altered β-globin while maintaining mRNA length.

Why A is correct:

• It describes complementary hydrogen bonding between the altered codon and tRNA anticodon GUG, incorporating a different amino acid per the genetic code's missense mutation rule.

Why the others are wrong:

• B: States the codon change but fails to explain how it alters the protein (no link to tRNA or amino acid).
• C: Repeats B's codon description with unnecessary "all transcripts" detail, without mechanistic explanation.
• D: Falsely implies the mutation creates a stop codon halting translation; it is a missense mutation allowing continuation.

Final answer: A