6.17—PCR amplification of DNA

PCR copies a selected DNA sequence in vitro. Primers define the region, heat separates strands, primers anneal at a lower temperature and thermostable DNA polymerase extends complementary strands.

Each cycle can double the target, so a tiny starting sample becomes enough for profiling or analysis. The polymerase must survive the high denaturation temperature.

A 20-cycle run can produce roughly a million copies from a single target molecule under ideal doubling; a missing primer or wrong annealing condition prevents selective amplification.

PCR amplifies the chosen region; it does not identify a person by itself. Contamination can be amplified too, so controls and the target sequence matter.