Which mutation typically results in a completely different protein due to reading frame shift?

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

Answer: (A)

The essential idea is that the genetic code is read in groups of three bases (codons). If nucleotides are inserted or deleted in a way that isn’t in multiples of three, the entire downstream reading frame shifts. This changes every codon that follows the mutation, so the amino acids produced from that point on are almost always completely different from the original sequence. Often this also creates a premature stop codon, truncating the protein or producing a nonfunctional product.

This is what a frameshift mutation does—an insertion or deletion that disrupts the reading frame. In contrast, a silent mutation changes a nucleotide without changing the amino acid, a missense mutation changes only one amino acid, and a nonsense mutation introduces a stop codon but does not shift the reading frame. Therefore, a frameshift mutation most typically yields a drastically altered, often nonfunctional protein.