A seminal advance was the discovery of the polymerase
chain reaction (PCR) by Kary Mullis in 1983 [18]. It
is a means of amplifying a single sequence of DNA to
produce many copies for a variety of purposes. A number
of different PCR techniques have been developed and
these are used for a variety of purposes. These include
diagnosis for clinical purposes in which characteristic
DNA template sequences in a sample are detected by a
known ‘reagent’ sequence. In this way DNA is synthesized,
which itself becomes the template for further synthesis
and the number of sequences is exponentially
amplified. PCR is also used for cloning in the course of
genetic manipulation.