 Mutation - DNA When a cell divides, it makes a copy of its DNA — and sometimes the copy is not quite perfect. That small difference from the original DNA sequence is a mutation.
 |  |  Mutation (1 of 4) Substitution A substitution is a mutation that exchanges one base for another (i.e., a change in a single "chemical letter" such as switching an A to a G).
 |  |  Mutation (2 of 4) Insertion Insertions are mutations in which extra base pairs are inserted into a new place in the genes.
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