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How PCR Has Revolutionized Forensics and Science

Sanzida Islam
School of Life Sciences
Independent University, Bangladesh

July 28th, 2017

The importance of the discovery of DNA (deoxyribonucleic acid) and its structure cannot be overstated. The influence of the resulting field of molecular biology on scientific and medical progress has been colossal. DNA is a macromolecule that carries the genetic code that determines the functions and characteristics of a living thing. All living organisms contain DNA (with the notable exception of some viruses). In the context of sexually reproducing species like ourselves, DNA is unique to every individual except identical twins. Genes are specific sequences of DNA that code for specific functions, or more specifically, for proteins that conduct specific functions. DNA is organized into long, threadlike structures called chromosomes, with each carrying hundreds of genes along its length at specific positions.

The polymerase chain reaction (PCR) is a laboratory technique that is used to make millions of copies of specific DNA in just a few hours. In other words, PCR is an efficient and cost-effective way to copy or amplify DNA from what can be very small amounts of initial samples.  After it was discovered in 1980s, PCR was rapidly taken up by the scientific community, and over the years, has become an essential and integral part of clinical, diagnostic, and basic science research. PCR has allowed a spectrum of advances ranging from the identification of novel genes and pathogens to the quantification of gene expression. Let us look at a couple of its specific applications.

PCR has been a boon for forensic scientists in crime scene investigations. Often during an investigation, insufficient DNA is available for analysis from whatever can be isolated from a few strands of hair, skin cells, blood or other bodily fluids left behind at the scene, thus impeding the application of modern DNA technologies to identify criminals and ultimately solve crimes. As we already know PCR represents a fast, cost-effective, and relatively easy solution to this problem.

Humans actually all share mostly the same DNA, but the uniqueness of individuals comes from specific sites or regions called polymorphisms, which vary greatly between people. We inherit unique sets of polymorphisms from our parents (the combination of which becomes our own) and these polymorphisms can be identified using DNA fingerprinting, which is a method of isolating and identifying variable sections of DNA. DNA fingerprinting relies on the fact that each individual has a characteristic motif of DNA. Hence, much like an actual fingerprint, the DNA fingerprint is distinct. This technique is mainly used to identify the probable origin of a body fluid or hair sample associated with a crime or crime scene, or to identify disaster victims, as in the Rana plaza collapse fire in a factory in Bangladesh. As mentioned earlier, in these cases, the DNA sample is usually limited. PCR is what allows the DNA to be amplified for the analysis by DNA fingerprinting.

In basic science research, PCR can be used to look for the presence of certain genes, and to amplify known sections of DNA for genetic modification. Genetic modification is the direct manipulation of an organism's genome using biotechnology. PCR allows us to generate large amounts of DNA for the purpose of manipulation. An example of genetic modification is insulin-producing bacteria. PCR produces large quantities of the gene that produces insulin, which are inserted into carriers or vectors called plasmids (circular pieces of DNA naturally found in bacteria). The plasmids are inserted into bacterial cells which then produce insulin.

PCR can be said to have triggered many valuable developments in several research and medical disciplines. The specific contribution of PCR in forensic studies and genetic engineering has brought about remarkable discoveries and applications, and it will remain second nature to molecular biologists, and indeed most biologists in general, for a long time.

Sanzida is second-year Microbiology student in the School of Life Sciences. She writes:

Quoting the renowned Francois Rabelais, “I go to seek a Great Perhaps”. I have found my passion in microbiology and I seek to reach to its depth because there is always something new to discover, more to learn and beneficial to give back to the people. Other than that I also enjoy the art of baking; there’s always some new flavours to cook up!

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