Template Strand Mutation Creates Stop Codon Steps:

• Identify stop codons in mRNA: UAA, UAG, UGA.
• Determine corresponding template DNA sequences using base complementarity (A↔U, T↔A, C↔G, G↔C): ATT for UAA, ATC for UAG, ACT for UGA.
• For premature stop, mutation must change a coding codon (transcribes to amino acid) to a stop codon template.
• Evaluate each option: original must code for an amino acid; mutated must be a stop template.

Why C is correct:

• ACC transcribes to UGG (tryptophan codon); ATT transcribes to UAA (stop codon), introducing premature termination per the genetic code.

Why the others are wrong:

• A: ATT (UAA stop) to ATC (UAG stop); both stops, no new premature termination.
• B: ACT (UGA stop) to ATC (UAG stop); both stops, no change to coding sequence.
• D: ATC (UAG stop) to ATG (UAC tyrosine codon); changes stop to coding, extends translation.

Final answer: C