The Frequency of Mutation Spontaneous mutation rate 1 in 109 replicated base pairs or 1 in 106 replicated genes Mutagens increase to 10-5 or 10-3 per replicated gene• Spontaneous mutation rate = 1 in 109 replicated base pairs or 1 in 106 replicated genes • Mutagens increase to 10–5 or 10–3 per replicated gene The Frequency of Mutation