A mutation that changes a codon to a stop codon is called what?

• A. Silent mutation
• B. Missense mutation
• C. Nonsense mutation
• D. Frameshift mutation

Answer: (C)

Changing a codon to a stop codon ends translation early, producing a shortened, often nonfunctional protein. This is called a nonsense mutation. The hallmark is the introduction of a premature stop signal that truncates the polypeptide.

Silent mutations change a nucleotide but leave the amino acid unchanged due to codon redundancy, so the protein sequence stays the same. Missense mutations alter one amino acid to a different one, which can affect protein function depending on the role of that residue. Frameshift mutations come from insertions or deletions that shift the reading frame, changing many downstream amino acids and typically altering protein structure and function, and often leading to an abnormal stop further downstream.