Name one type of mutation that affects a single nucleotide.

A point mutation is a specific type of mutation that involves the alteration of a single nucleotide in the DNA sequence. This can occur in various ways, such as a substitution where one nitrogen base is replaced by another. Point mutations can lead to changes in the amino acid sequence during protein synthesis, potentially impacting the protein's function depending on where the mutation occurs and the nature of the substitution.

Other types of mutations listed, such as insertion and duplication mutations, involve adding extra nucleotides to the sequence, while frame-shift mutations result from changes in the number of nucleotides, usually causing a shift in the reading frame of the genetic code. These mutations impact larger sections of DNA rather than a single nucleotide, highlighting why the point mutation is the correct answer for identifying a mutation that affects just one nucleotide.