Spontaneous mutations: The bases (A, T, G, C) in DNA are altered or lost due to unrepaired replication errors or random molecular events. For example, the loss of an amino group from cytosine, a normal base found in DNA, leads to the production of uracil, a base not normally found in DNA. If this change is not detected and reversed, a mutation can result. Occasionally, an entire base can be lost as a result of the cleavage of the bond between the DNA backbone and the base. This leads to a gap in the DNA double-helix, which, if not repaired, can lead to a mutation the next time the DNA is copied (i.e. during replication).
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