What is the consequence of a frameshift insertion or deletion?

• A. No effect
• B. Only affects noncoding regions
• C. Shifts reading frame, producing different amino acids and typically premature stop codon
• D. Increases translation efficiency

Answer: (C)

Frameshift mutations happen when nucleotides are inserted or deleted in a coding sequence in a number not divisible by three. Because the genetic code is read in triplets, this changes the grouping of codons from the mutation point onward. The downstream amino acid sequence becomes entirely different, and it’s common to encounter a premature stop codon along the new reading frame. The resulting protein is usually truncated and nonfunctional because the altered amino acids disrupt folding and activity. This is why a frameshift has such a dramatic impact. The other possibilities—no effect, only affecting noncoding regions, or increasing translation efficiency—don’t reflect how shifting the reading frame alters every codon after the mutation and nearly always produces a faulty protein.