A DNA sample can be copied many times (amplified) in vitro by the polymerase chain reaction PCR
in a 3-step cycle.
- Heating to denature the DNA:
separate the double-stranded molecule into single strands.
- Annealing to allow complementary primers to form by cooling the mixture.
- Extension to replicate each strand with a heat-resistant DNA polymerase and nucleotides.
During each PCR cycle, the target DNA sequence is doubled.