How can a frameshift mutation affect protein coding?

• A. It adds new amino acids without affecting reading frame.
• B. It shifts reading frame, altering downstream amino acids and often creating a premature stop.
• C. It only affects noncoding regions.
• D. It always increases protein stability.

Answer: (B)

Frameshift mutations change how the genetic code is read because codons are read in triplets. When nucleotides are inserted or deleted in numbers not divisible by three, every downstream codon is regrouped, so the amino acids added after the mutation are different. This often introduces a new stop codon along the way, truncating the protein and usually yielding a nonfunctional product. An in-frame insertion or deletion would add or remove whole amino acids without shifting the reading frame, which is not what a frameshift does. Frameshift effects occur in the coding region and disrupt the protein sequence rather than simply stabilizing it; they’re more likely to weaken or abolish function than to improve it.