Acronym for "Polymerase Chain Reaction", this is a technique used to amplify DNA exponentially, which is to say, to make many copies of DNA very quickly. This is a relatively simple process that requires a few basic components in a test tube and a small series of temperature changes to efficiently copy the DNA.

Briefly, in a small, thin walled test tube we place the following components: DNA template to copy, heat resistant DNA polimerase, small DNA primers, DNA deoxynucleotide triphosphate mix, and a buffer solution. Once mixed, the test tube is placed in a machine, called a thermocycler, that can quickly change the temperature of the mixture to allow the DNA polymerase to use the DNA primers as guides to copy precise segments of the DNA template.

In short, a PCR cycle starts at a high "melting", or denaturing temperature (around 95 deg C) to separate the DNA strands from the template. This is followed by a decrease in temperature (usually somewhere between 50-60 deg C) to allow the two primers (which have been carefully designed to be complementary to sequences on each DNA strand from the template) to anneal and provide the DNA polymerase with a starting point for strand elongation. Actual strand elongation, or extension (the process of copying the DNA) is facilitated by raising the temperature to around 72 deg C, the optimal temperature of the DNA polymerases used in PCR. This last temperature change ends the PCR cycle, and doubles the DNA sequence bounded by both primers. Geometric expansion of the bounded DNA sequence can be attained by repeating the PCR cycle multiple times. Since there is a doubling of DNA amount each cycle, no more than around 35 cycles are needed to generate all the DNA needed for typical analyses and experiments.