Applications of PCR:

Polymerase chain reaction already has very widespread applications and new uses are being devised on a regular basis. Some and definitely not all of the applications are given as follows:

-   PCR can amplify a single DNA molecule from a complex mixture, largely preventing the requirement to use DNA cloning to prepare that molecule.  Different of the methods can similarly amplify a specific single RNA molecule from a complex combination.

-   DNA sequencing has been widely simplified using Polymerase chain reaction, and this application is now general.

-   Through using suitable primers it should be possible to use PCR to create point mutations, deletions and insertions of target DNA that greatly facilitates the analysis of gene expression and function.

-   Polymerase chain reaction is exquisitely sensitive and can amplify vanishingly small amounts of DNA.  Therefore,  using  appropriate   primers  very  little  amounts  of  specified viruses    and bacteria can be detected  in tissues and making  PCR invaluable  for medical diagnosis.

-   Polymerase chain reaction is now invaluable for characterizing medically important DNA samples.

For instance, in screening for human genetic disease that is rapidly replacing the use of RFLPs. The Polymerase chain reaction screen is based on the analysis of microsatellites.  These are tri- , di- and tetranucleotide  repeats in the DNA of the type (CA)_n   or (CCA)_n   where n is a number from 10 to more than 30. Microsatellites can be used as markers in the same way that RFLPs were used in the past. Thus two primers are chosen that bind to the DNA flanking the microsatellite.  PCR is then hold out and the various sizes of microsatellite give different sizes of amplified DNA fragments that can then be used as screening markers.  The technique is very quick, reliable and uses very small amounts of clinical material.

-   Because of its extreme sensitivity, PCR is now fundamentally very important to forensic medicine. It is even possible to use PCR to amplify the DNA from a single human hair or a microscopic drop of blood left at the scene of a crime to allow detailed characterization.