Amplification by PCR has sequence-dependence efficiency,
especially the sequence that binds to primers. If one sequence is amplified 10%
more than another in one round, it will be 1.130 = 17.4 x more
abundant after 30 rounds. This effect is most important when the sequence has
one or more mismatches with the primer. With one mismatch, amplification
efficiency is usually significantly less, and with two or more mismatches the
sequence may not be amplified to detectable levels.