Which type of mutation changes a codon to a stop codon?

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

Answer: (C)

A nonsense mutation is the type that changes a codon into a stop codon, causing translation to terminate early and producing a truncated, often nonfunctional protein. This happens when a single nucleotide change converts an amino-acid codon into one of the three stop codons, so the ribosome stops adding amino acids at that point.

To connect the others: a silent mutation alters the DNA but not the amino acid due to codon redundancy, so the protein sequence stays the same. A missense mutation changes one amino acid to a different one, altering the protein’s structure or function rather than stopping translation. A frameshift mutation results from insertions or deletions that shift the reading frame, changing many downstream amino acids and typically altering the entire protein; it can sometimes introduce a premature stop, but its defining feature is the shift in the reading frame, not the creation of a stop codon itself.

So the change that directly turns a codon into a stop codon is a nonsense mutation.