Which mutation results in no change to the amino acid sequence?

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

Answer: (B)

The idea here is that some DNA changes do not alter the amino acid that a codon encodes because the genetic code is redundant. A silent (synonymous) mutation changes the DNA sequence but keeps the same codon meaning, so the same amino acid is added during translation. For example, a codon that normally codes for glutamate can shift from GAA to GAG, and both codons still specify glutamate. Because the produced amino acid sequence stays the same, the protein sequence is unchanged.

In contrast, a missense mutation changes a codon to one that encodes a different amino acid, altering the protein’s sequence and potentially its function. A nonsense mutation creates a stop codon, truncating the protein. A frameshift mutation results from inserting or deleting nucleotides not in multiples of three, shifting the entire reading frame and usually producing a drastically different, nonfunctional protein. Silent mutations are often neutral with respect to protein function, though in some cases they can affect mRNA structure or splicing.