Name two common types of point mutations.

• A. Substitution mutations, such as missense and nonsense (and sometimes silent)
• B. Insertions and deletions
• C. Duplications and translocations
• D. Inversions and transversions

Answer: (A)

Point mutations are changes that affect a single nucleotide in DNA. The most common type is a substitution, where one base is replaced by another. What makes substitutions powerful is how they can alter the codon that encodes a protein: a missense change swaps one amino acid for another, a nonsense change creates a premature stop codon, and sometimes a silent change doesn’t alter the amino acid at all because of the genetic code’s redundancy. This is why substitution mutations, with these possible outcomes, are the best match for common point-mutation types. Other listed possibilities involve insertions, deletions, or larger rearrangements, which are not point mutations since they affect more than a single nucleotide.