擴大DNA量的技術，其中目標DNA的兩側序列是知道的。短的DNA片段（引物）通過特殊的TAQ酶結合在側翼序列上并在兩個引物間復制序列。循環升溫分離DNA雙鏈，降溫使引物結合，再升溫使酶能復制DNA。這樣每一循環產生雙倍DNA。這一反應通常是在一可調控的溫箱中或PCR儀中進行，對所有的DNA進行30到35個循環擴增。PCR十分敏感，可以從一個DNA分子擴增到微克的量。靶子DNA可以是任何來源，所以用PCR來擴增DNA的方法可以用于研究，克隆和司法簽定，它們都可以利用PCR的極度敏感性。

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