A mutation that shifts the reading frame of the genetic message; includes insertions and deletions

• A. Reading frame
• B. Insertion mutation
• C. Deletion mutation
• D. Frame-shift mutation

Answer: (D)

Shifts in how the genetic message is read happen when nucleotides are added or removed in a way that changes how bases group into codons of three. This specific kind of mutation is called a frame-shift mutation. Because the reading frame is altered, every codon downstream is read differently, producing a completely different sequence of amino acids and often a nonfunctional protein or a premature stop signal.

If the insertion or deletion consists of a number of nucleotides that is a multiple of three, the reading frame stays the same, and only the length of the protein changes—not the grouping of codons. The term describing that shift caused by insertions or deletions is frame-shift, which is why it’s the best fit for the description.