What in PCR for?

In just 20 years from its invention, the PCR method, thanks to the great progress of technology and research, can now be used to find a solution to problems that first could not be solved.
Due to its great sensitivity, PCR is presently applied whenever very small quantities of DNA are involved. In the field of medical diagnosis, the amount of DNA contained in a drop of blood is more than sufficient to amplify and verify the possible presence of a genetic mutation associated to a hereditary sickness. With this method tumour cells can be identified, for example in the case of liquid tumours that are very difficult to locate. Moreover, since DNA is a very stable substance, even after thousands of years, as in the case of Egyptian mummies, it is possible to study it with the PCR method. Thanks to the discovery of this method, a new scientific discipline was born: paleobiology that involves the study of DNA in plant and animal fossils.
In conclusion, it would be impossible to even just outline all the possible variations of the PCR method and their respective fields of application, so in this context we will just consider some examples.
A help in the Police and Carabinieri Corps investigations
Even in courtrooms now it is normal to talk about DNA analyses using the PCR method. In forensic medicine, the finding of organic material (such as hair, skin fragments or blood) on the scene of the crime or of an accident allows the identification of the victim or of the culprit.
In the Biological Investigations Laboratory of the Forensic Department of Police in Rome (Laboratorio d’Indagini Biologiche del Servizio Polizia Scientifica di Roma), researchers have created a PCR method suitable for solving those crime cases which apparently seem to have no clues on the crime scene. The possibility, on the part of the forensic team, of discovering some clues on how the mysterious facts took place and the identity of the culprits has greatly increased from when it has become easier to analyse the DNA. Moreover, work is being carried out to create an Italian DNA data bank in which complete DNA profiles of dangerous individuals or those who are being investigated,  are kept. From around 1996, the application of the PCR technique allows the analysis of DNA even in those cases in which the samples are very small or in bad conditions such as hair fragments or very old bone material.
American television serials and lately even Italian ones often show teams of biologists, biochemists and other scientists, side by side with detectives, carrying out investigations that are far from reality. In fact, on the scene of the crime, it is normal to see expert biologists in white suits and half masks scraping at walls, collecting biological samples from tooth brushes or discovering traces of blood or sperm that were hidden or invisible.
Discovering unknown micro-organisms
From the environmental point of view, PCR is applied to trace undesired microbes in drinking water, rivers and sea water.
To monitor and identify a microbial community, samples of micro-organisms whose genus and species are unknown must be collected from their natural environment and possibly cultivated in the laboratory. To get to know the bacteria collected, the utilization of the different PCR methods can be really decisive because it permits the sure identification of their DNA.
The advantage of utilizing methods that analyse and recognise the DNA of bacteria is that the experiment times are much shorter than when classic microbiology techniques are used; moreover, the results are more precise and repeatable. In fact, many groups of micro-organisms that live in very different surroundings have been discovered and studied in acceptable times and with reliable results: sea waters containing oil or other hydrocarbons that are metabolized (eaten) by some species of bacteria, soil polluted with zootechnical sewage (animal sludge), milk, cheese and natural environments in which food products are left to season.

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