How does the test work?
The Polymerase Chain Reaction (PCR), is the technique used to detect small amounts of DNA and make enough copies of it to be detectable.
All cells, bacteria and viruses contain DNA that is unique to them. When a sample arrives for testing it is prepared by a lengthy digestion and purification process to release all DNA from that sample.
The prepared sample is then added to a PCR mixture containing small pieces of DNA (primers) which match the DNA we are testing for, building blocks of DNA, and a polymerase enzyme which can join the blocks together to make copies of DNA.
If there is DNA that we are testing for in the sample, the matching primers will stick to the DNA, and the polymerase will start making copies of the DNA. Each copy of DNA can then bind the matching primers and another two copies can be made. This chain reaction is repeated up to forty times, resulting in a comparatively huge amount of DNA at the end of the cycle generated from the little that was originally present.
In most of our disease tests we use a fluorescent marker which only fluoresces in the presence of the amplified DNA, the more DNA present the more fluorescence there will be.
If the sample does not contain the DNA we are testing for, there is nothing for the primers to stick to so the polymerase will not make any DNA and there will be no fluorescence.
In our sexing tests when the PCR is finished, the samples are run through a gel matrix and put under a UV light. Any DNA present will glow in bright band(s) which indicate that DNA has been successfully extracted, for female samples we see two bands and for male samples we see only one.