The DNA poly- merase is the key enzyme that links individual nucleotides together to form the PCR product. The nucleotides include the four bases—adenine, thymine, cytosine, and guanine (A, T, C, G)—that are found in DNA. These act as the building blocks that are used by the DNA polymerase to create the PCR product. The polymerase chain reaction (PCR) has been employed extensively in the medical and biological sciences since it was formally introduced at the Cold Spring Harbor 51st Symposium on Quantitative Biology (Mullis et aI., 1986) and it has repeatedly resulted in three complaints. The first is that PCR has made DNA research boring. Polymerase Chain Reaction TABLE 1. Primer design aProperty Optimal design Base composition G+C content should be between 40% and 60%, with an even distribution of all four bases along the length of the primer (e.g., no polypurine or polypyrimidine tracts and no dinucleotide repeats). the polymerase chain reaction. In 1986 he became the director of molecular biology at Xytronyx, Inc. Today Mullis works in La jolla, Calif., as a private con-sultant on polymerase-chain-reaction technology and nucleic acid chemistry. 56 SCIENTIFIC AMERICAN April 1990 by Kary B. Mullis tal tissue specimen, from a single hu-man hair, from a drop Polymerase chain reaction (PCR) was invented by Mullis in 1983 and patented in 1985. Its principle is based on the use of DNA polymerase which is an in vitro replication of specific DNA sequences. PCR is a very powerful amplification tool so very little DNA is actually required (usually in the pg range). To copy DNA, all polymerases require a short sequence of nucleotides to provide a free 3'OH group. Within cells of most organisms enzymes unwind the duplex and then RNA polymerase adds priming nucleotides. POLYMERASE CHAIN REACTION (PCR) The polymerase chain reaction (PCR) is a technique used to amplify specific segments of DNA that may range in size from ca. 200 - 2000 or more base pairs. Two recent papers that summarize the development and applications of PCR and discuss its specific applications to Organismal and Population Biology are Mullis. K. Polymerase Chain Reaction (PCR) Paul C Winter, Belfast City Hospital, Belfast, UK The polymerase chain reaction is a techniq ue that allows DNA molecules of interest (usually gene sequences) to be copied in a simple enzyme reaction producing a sufficient quantity of the copied DNA for detailed analysis or manipulation. The The polymerase chain reaction (PCR) is the cardinal laboratory technology of molecular biology. Arguably one of the most powerful laboratory techniques ever discovered, PCR combines the unique attributes of being very sensitive and specific with a great degree of flexibility. Figure 1: The polymerase chain reaction: (A) the reaction mix-ture and (B) the sequence of events. (c) The third and final stage is an extension reaction carried out by an added thermostable DNA-poly-merase, an enzyme able to synthesize a complemen-tary copy of the initial single strands by extension of the The Polymerase chain reaction (PCR), first envisaged in 1984 by Kary Mullis, has revolutionized life sciences and has become an essential technique in many aspects of science, including clinical diagnostics, forensics and genetic engineering. Kary Mullis eventually received the Nobel Prize in Chemistry in 1993. "Polymerase Chain Reaction (PCR) Market Overview: The global COVID-19 crisis has greatly increas