Fig. 1. Schematic of the polymerase chain reaction. Each cycle of the polymerase chain reaction (PCR) includes heat denaturation of the double-stranded DNA template into single strands, annealing of an oligonucleotide primer complementary to sequence being amplified, and extension of the annealed primer using a thermostable DNA polymerase and nucleotide triphosphates. Repeated cycles results in exponential, sequence specific amplification of the original target.