Which mutation type is most likely to alter many amino acids downstream if it occurs early in a gene?

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

Answer: (C)

A frameshift mutation shifts the reading frame of the gene by inserting or deleting nucleotides not in multiples of three. Once the frame is shifted, every codon downstream is read incorrectly, so a large stretch of amino acids is changed. If this happens near the start of the gene, most of the protein sequence becomes wrong, and a premature stop is common, producing a truncated, nonfunctional product. Silent mutations don’t change amino acids, so there’s no downstream alteration. Missense mutations change a single codon and affect only one amino acid. Nonsense mutations create an early stop, truncating the protein rather than altering many downstream residues. Therefore, a frameshift early in a gene causes the most widespread downstream changes.