PCR, short for polymerase chain reaction, is a method for in vitro enzymatic synthesis of specific DNA fragments, consisting of 1 cycle of high temperature denaturation, low temperature annealing, and moderate temperature extension reactions, which are cycled to enable rapid amplification of the target DNA. With the characteristics of high specificity, high sensitivity, easy operation and time saving, it can be used not only for basic research such as gene isolation cloning and nucleic acid sequence analysis, but also for diagnosis of diseases and anywhere DNA and RNA are available. PCR is also known as cell-free molecular cloning or specific DNA sequence in vitro primer directed enzymatic amplification technique.