 If the target DNA contains an allele complementary to the probe's 3’ base, the target DNA will completely hybridize to the probe, allowing DNA polymerase to extend from the 3’ end of the probe.This is detected by the incorporation of the fluorescently labeled dNTPs onto the end of the probe.If the target DNA does not contain an allele complementary to the probe's 3’ base, the target DNA will produce a mismatch at the 3’ end of the probe and DNA polymerase will not be able to extend from the 3' end of the probe.