Since infectious and genetic diseases are characterized by the presence of foreign (viral, fungal or bacterial) or aberrant DNA respectively, the diagnostic use of PCR is quite a helpful technique.
The polymerase chain reaction is a rapid procedure for amplification of specific DNA sequences. Three basic steps are performed:
(1) thermal denaturation of double stranded DNA,
(2) annealing of oligodeoxynucleotide primers, and
(3) extension of the annealed primers by DNA synthesis.
The PCR technique became practical after discovery of a thermostable DNA polymerase (Taq), isolated from the bacterium
Thermus aquaticus, capable of withstanding the high temperatures necessary to separate the DNA strands.
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