Which term describes a point mutation where one base is replaced by another?

• A. Point mutation
• B. Insertion mutation
• C. Substitution mutation
• D. Deletion mutation

Answer: (C)

A single-nucleotide change where one base is replaced by a different one is called a substitution mutation. This is a specific type of point mutation, which are small changes to the DNA. The key idea is that the length of the DNA sequence doesn’t change; only the identity of that one base does. Insertion mutations add an extra base, changing the length, and deletion mutations remove a base, also changing the length. Substitution can alter the codon in a gene and may change the amino acid (a missense change), create a stop signal (nonsense), or, in some cases, still code for the same amino acid (silent).