For example, during replication, a thymine nucleotide might be inserted in place of a guanine nucleotide. With base substitution mutations, only a single nucleotide within a gene sequence is ...

A sugar molecule, a base, and a phosphate molecule group together to make up a nucleotide ... Cytosine (C) will "pair" to guanine (G), and adenine (A) will "pair" to thymine (T).