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.