Method of rapidly amplifying a given DNA sequence. Uses short primers which anneal to both ends of the sequence, acting as a template for DNA polymerase to fill in the intervening sequence. Uses a thermocycler to raise the temperature, causing the DNA strands to melt (separate). The temperature then drops, new primers anneal, and the process repeats. Every cycle doubles the amount of DNA present, allowing infinite amplification of a given sequence. This has allowed techniques like DNA fingerprinting to become useful, as a very small sample of DNA from a crime scene can be amplified and used to identify a suspect. Invented by Kary B. Mullis, a breakthrough for which he won the Nobel Prize in Chemistry.