Polymerase Chain Reaction (PCR) is a molecular biology technique that allows for quick replication of DNA. With PCR, minute quantities of genetic material can be amplified millions of times within a few hours allowing for the rapid and reliable detection of genetic markers. PCR is a three-step process, referred to as a cycle, that is repeated a specified numbers of times (usually between 30 and 40 times). One PCR cycle consists of the following steps:

Step 1: Denaturation by Heat
Heat (usually >91°C) separates double-stranded DNA into two singles strands. Since the hydrogen bonds linking the bases to one another are weak, they break at high temperatures, whereas the bonds between deoxyribose and phosphates, which are stronger covalent bonds, remain intact.

Step 2: Annealing V Primer Binding to Target
Two primers are included in the PCR, one for each of the complementary single DNA strands that was produced during denaturation. They anneal (bind) to the complementary sequence and mark the beginning of the DNA target sequence. To allow the primers to anneal to the target sequence with high sequences with high specificity, annealing usually takes place between 40°C and 65°C, depending on the length and base sequence of the primers.

Step 3: Extension
Once the primers annual to the complementary DNA sequences, the temperature is raised to approximately 72°C and the enzyme Taq DNA polymerase begins the synthesis process at the 3' end of the primer in the 5' to 3' direction. Taq DNA polymerase synthesizes new double stranded DNA molecules by facilitating the binding and joining of the complementary nucleotides that are free in solution (dNTPs).