The polymerase chain reaction (PCR) is an in vitro method for selectively amplifying a defined region of DNA through repeated thermal cycling of three steps: denaturation, in which heat separates the double-stranded template; annealing, in which short synthetic oligonucleotide primers complementary to the flanking sequences bind at reduced temperature; and extension, in which a thermostable DNA polymerase synthesizes new strands 5′→3′ from the primers using free nucleotides. Because each cycle doubles the number of copies of the targeted region, amplification is exponential in cycle number, and because the primer pair defines both boundaries, the product converges after early cycles on a discrete fragment delimited exactly by the primer positions. PCR belongs to molecular biology and molecular genetics and provides the enabling technique wherever a specific sequence must be isolated from a complex genome for cloning, analysis, or detection.
The polymerase chain reaction (PCR) is an in vitro method for selectively amplifying a defined region of DNA through repeated thermal cycling of three steps: denaturation, in which heat separates the…