In order to work with DNA in the laboratory we often need to produce that DNA in a larger quantity. In addition, a longer DNA molecule like a whole human chromosome is difficult to work with, and we rather want to focus on a smaller region of DNA. In a classic cloning experiment a smaller DNA fragment is introduced into a circular plasmid DNA, which is allowed to replicate within bacterial cells. Once the bacterial cells have grown to a certain density, these cells may be isolated by centrifugation and the plasmid DNA purified from the bacterial cells. This is a somewhat time-consuming procedure, but there is an alternative method in gene technology that is more convenient. Thus, our third example of gene technology is the polymerase chain reaction (PCR), invented by Kary Mullis in 1984 (Mullis et al., 1986).

What is PCR?

PCR is one of the most widely used techniques in DNA technology. As in traditional cloning it is a means to amplify a shorter region of DNA, i.e. to produce a distinct region of DNA in a large quantity. However, PCR is carried out in a simple test tube reaction where DNA is amplified with the help of the enzyme DNA polymerase. Another technical advantage of PCR compared to conventional cloning in some bacterial host is that the DNA product is relatively pure.