Polymerase chain reaction (PCR) is a molecular diagnostic tool that allows for in vitro amplification of DNA at a rapid pace. The steps of PCR are: denaturation, annealing, and extension. DNA doubles during each PCR cycle, resulting in exponential accumulation of the targeted DNA fragment. The ability to rapidly amplify a specific nucleic acid sequence in a short period of time has revolutionized molecular diagnostics.
A major advantage of PCR is that only a small amount of initial intact genomic DNA is required. PCR can be effective with only a single strand of intact DNA. This is often critical for forensic analysis where only trace amounts of DNA are available. PCR has also been used to amplify and analyze ancient DNA for anthropologic and archeological purposes.
PCR augments many common laboratory methods such as Southern blotting. These techniques require a large amount of DNA. PCR can be used to supply these techniques with the needed amounts of specific DNA. PCR can also be incorporated into DNA sequencing and genetic fingerprinting.