A mutation caused by inserting a single nucleotide into a coding sequence most likely results in which type of mutation?

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

Answer: (A)

In protein-coding sequences, codons are read in groups of three bases. Inserting a single nucleotide shifts this reading frame from that point onward, so every downstream codon changes. This drastic alteration typically changes many amino acids and often introduces a premature stop, producing a nonfunctional protein. That is the hallmark of a frameshift mutation. Silent mutations involve changes that don’t alter the amino acid sequence, missense mutations change one amino acid by a single-base substitution without shifting the frame, and nonsense mutations create a stop codon (often from substitutions, though context can vary). So the insertion of one nucleotide most likely causes a frameshift mutation.