silent mutation

A silent mutation is a change in the DNA that does not change the amino acid the codon specifies, so the protein comes out identical. It is like a typo that still spells the same word in a different accepted way — the reader notices nothing.

This is possible because the genetic code is redundant: most amino acids are encoded by several different codons that differ usually in their third base. A substitution that swaps one synonymous codon for another, often called a synonymous mutation, leaves the protein sequence untouched even though the DNA sequence has changed.

Calling such mutations truly silent is a useful simplification but not always exact. A synonymous change can subtly affect how fast a gene is translated, how messenger RNA is spliced or folded, or how stable the transcript is. Most are indeed neutral, yet biologists no longer assume every silent mutation is entirely without effect.