Now and again a scientific discovery is made that changes the whole course of the development of a subject. In the field of molecular biology we can identify several major milestones – the emergence of bacterial genetics, the discovery of the mechanism of DNA replication, the double helix and the genetic code, restriction enzymes, and finally the techniques of recombinant DNA. Many of these areas of molecular biology have been recognised by the award of the Nobel prize in either Chemistry or in Medicine and Physiology. Some of these key discoveries are listed in Table 7.1.

The topic of this chapter is the polymerase chain reaction (PCR), whic h was discovered by Kary Mullis and for which he was awarded the Nobel prize in Chemistry in 1993. The PCR technique produces a similar result to DNA cloning – the selective amplification of a DNA sequence – and has become such an important part of the genetic engineer's toolkit that in many situations it has essentially replaced traditional cloning methodology. In this chapter we will look at some of the techniques and applications of PCR technology.

The (short) history of the PCR

The essentials for PCR were in place by the late 1970s. In 1979 Kary Mullis joined the Cetus Corporation, based in Emeryville, Califor nia. He was working on oligonucleotide synthesis, which by the early 1980s had become an automated and somewhat tedious process. Thus, his mind was free to investigate other avenues.