Predicting mutation effects

A mutation is a change in DNA sequence. Its effect depends on location and context. In a protein-coding region, a substitution may be synonymous, change an amino acid, or introduce a stop signal. Regulatory changes can alter gene activity without changing a protein's sequence. An insertion of one nucleotide within a translated coding region usually shifts the reading frame downstream. An insertion of three nucleotides preserves the frame, though adding an amino acid can still affect protein function. Frame preservation does not guarantee no effect.