Process of DNA Testing

There are various ways to test DNA. One very common method used in various settings, including forensic and paternity testing labs, is polyermase chain reaction or PCR. Using this method, DNA is extracted from sample cells and primers are used to locate the sequence of interest on the DNA strand. This sequence is then amplified to create many million and even billion of copies.

In the case of paternity testing, somatic, or body cells from the possible father are obtained by taking a swab of the inner lining of the father's mouth. The DNA is extracted from the cells and is then amplified, creating many copies. These copies are then compared to those of the offspring to see if there is a close match. Although PCR is less time-consuming and cheaper than another method called RFLP, it is very suspectible to contamination and care must be exercised during the entire testing process.

In RFLP, or Restriction Fragment Length Polymorphism, a restriction enzyme is used. Obtained by bacteria that can "cut" DNA at a particular location, restriction enzymes cut many copies of the DNA sequence of interest. The sequence is then separated according to size using gel electrophoresis. Next, "blotting" is performed in which a film is applied to the gel and stained allowing the different bars, representing different sequences, to be seen. This prevents any further migration of the DNA sequences in the gel. A DNA probe is then attached to the sequence of interest.

As in PCR, the DNA copies are compared to others in the population to determine if there are a "match." Rather than just one person's DNA, in the case of paternity testing, DNA from a large population needs to be used in order to effectively compare the lab sample to those in the population. This, along with the increased cost and time required, is the reason that RFLP is no longer widely used as it had been.