扩大DNA量的技术，其中目标DNA的两侧序列是知道的。短的DNA片段（引物）通过特殊的TAQ酶结合在侧翼序列上并在两个引物间复制序列。循环升温分离DNA双链，降温使引物结合，再升温使酶能复制DNA。这样每一循环产生双倍DNA。这一反应通常是在一可调控的温箱中或PCR仪中进行，对所有的DNA进行30到35个循环扩增。PCR十分敏感，可以从一个DNA分子扩增到微克的量。靶子DNA可以是任何来源，所以用PCR来扩增DNA的方法可以用于研究，克隆和司法签定，它们都可以利用PCR的极度敏感性。

A technique used to “amplify” (or generate large amounts) of DNA for which the “flanking” sequences (those sequences directly on either side of the target DNA) are known. Short complementary DNA fragments (“primers”), which bind these flanking sequences are used by a special enzyme (Taq polymerase which is active at high temperatures) to copy the sequence in-between the primers. Cycles of heat to break apart the DNA strands, cooling to allow the primers to bind, and heating again to allow the enzyme to copy the intervening sequence, lead to a doubling of DNA at each cycle. The reactions are typically carried out on a regulated heating block, or PCR machine, and consist of 30-35 cycles of repeated amplification of all the DNA present. PCR is very sensitive, allowing a single molecule of target DNA to be amplified to microgram amounts of DNA. The target DNA can be of any origin, and so PCR is used to amplify DNA for use in research, cloning and forensics, each of which takes advantage of PCR’s extreme sensitivity