Polymerase chain reaction (PCR) is a molecular biology technology used to amplify specific DNA fragments. It can be regarded as a special DNA replication in vitro. The biggest feature of PCR is that it can greatly increase a small amount of DNA. Therefore, as long as a little DNA can be isolated, it can be amplified and compared by PCR, whether it is the remains of Paleontology and historical figures in fossils, or the hair, skin or blood left by the murderer in the murder several decades ago. This is also the power of "trace evidence".
PCR uses DNA denaturation at high temperature of 95 ° C in vitro to become a single strand. At low temperature (often about 60 ° C), primers and single strand are combined according to the principle of base complementary pairing, and then adjust the temperature to the optimal reaction temperature of DNA polymerase (about 72 ° C). DNA polymerase synthesizes the complementary strand along the direction of phosphoric acid to pentose (5 '- 3'). The PCR instrument based on polymerase is actually a temperature control equipment, which can well control the denaturation temperature, renaturation temperature and extension temperature
