What term describes a mutation that changes a single nucleotide but does not change the amino acid produced?

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

Answer: (A)

A single-nucleotide change that does not alter the amino acid is due to the redundancy of the genetic code. Many amino acids are encoded by more than one codon, so if the nucleotide change produces a different codon that still codes for the same amino acid, the resulting protein sequence stays the same. This kind of mutation is called a silent mutation. For example, a codon for glycine can be GGU, GGC, GGA, or GGG; changing GGU to GGC changes the DNA sequence but not the amino acid. This is different from mutations that shift the reading frame or create a stop codon, or that replace one amino acid with another.