DNA Testing

Genetic fingerprinting or DNA profiling is a techniques used to distinguish between individuals using only samples of their DNA. It was invented by Sir Alec Jeffreys in 1985. Two humans will have the vast majority of their DNA sequence in common. Genetic fingerprinting exploits highly variable repeating sequences called minisatellites. Two unrelated humans will be unlikely to have the same numbers of minisatellites at a given locus. In STR profiling, which is distinct from DNA fingerprinting, PCR is used to obtain enough DNA to then detect the number of repeats at several loci. It is possible to establish a match that is extremely unlikely to have arisen by coincidence, except in the case of identical twins, who will have identical genetic profiles.

Genetic fingerprinting is also used in such applications as identifying human remains, paternity testing, matching organ donors, and also been used to generate hypotheses on the pattern of the human diaspora in prehistoric times.

PCR Analysis

The polymerase chain reaction (PCR) is a biochemistry and molecular biology technique for isolating and exponentially amplifying a fragment of DNA, via enzymatic replication, without using a living organism (such as E. coli or yeast). As PCR is an in vitro technique, it can be performed without restrictions on the form of DNA, and it can be extensively modified to perform a wide array of genetic manipulations. Invented in 1983 by Kary Mullis, PCR is now a common technique used in medical and biological research labs for a variety of tasks, such as the sequencing of genes and the diagnosis of hereditary diseases, the identification of genetic fingerprints which is used in DNA Paternity Testing.

With the invention of the polymerase chain reaction (PCR), DNA fingerprinting took huge strides forward in both discriminating power and ability to recover information from very small starting samples. PCR involves the amplification of specific regions of DNA using a cycling of temperature and a thermostable polymerase enzyme along with sequence specific primers of DNA.

OQPS supply kits that use single nucleotide polymorphisms (SNPs) for discrimination. Our kits use PCR to amplify specific regions with known variations and hybridize them to probes anchored on cards, which results in a colored spot corresponding to the particular sequence variation.

PCR is used to amplify specific regions of a DNA strand. This can be a single gene, just a part of a gene, or a non-coding sequence. Most PCR methods typically amplify DNA fragments of up to 10 kilo base pairs (kb), although some techniques allow for amplification of fragments up to 40 kb in size.

The PCR is carried out in small reaction tubes (0.2-0.5 ml volumes), containing a reaction volume typically of 15-100 µl, that are inserted into a thermal cycler. This is a machine that heats and cools the reaction tubes within it to the precise temperature required for each step of the reaction. Most thermal cyclers have heated lids to prevent condensation on the inside of the reaction tube caps. Alternatively, a layer of oil may be placed on the reaction mixture to prevent evaporation.

when these fragments are run out on an agarose gel they produce a specific pattern of bands. With the use of PCR, in theory, only a single DNA strand is needed, providing very high sensitivity to this technique, although such sensitive amplification increases the risk of confounding results due to possible contamination with, and amplification of, DNA from extraneous sources. There are different PCR-based methods for fingerprinting, summarized in Genetic fingerprinting. The overall pattern of PCR-generated DNA fragments after gel electrophoresis and visualization by ethidium bromide staining (or hybridization with a DNA probe after Southern blotting), can be considered a DNA fingerprint analogous to the fingerprint pattern unique to each individual.

Although these resulting 'fingerprints' are unique , genetic relationships, for example, parent-child or siblings, can be determined from two or more genetic fingerprints, which can be used for paternity tests (Fig. 4). A variation of this technique can also be used to determine evolutionary