An insertion leading to a frameshift results in which mutation?

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

Answer: (B)

An insertion that changes the reading frame disrupts how codons are grouped into triplets. The genetic code is read three nucleotides at a time, so adding one nucleotide shifts all downstream codons, altering which amino acids are specified and often creating an early stop. This change is called a frameshift mutation. If the insertion were a multiple of three, the frame wouldn't shift and you'd get an in-frame insertion instead, not a frameshift. In contrast, a point mutation is a single base substitution, a silent mutation doesn't change the amino acid sequence, and a nonsense mutation is a substitution that creates a premature stop codon.