All biological materials, no matter the age or how they were stored, can be tested for DNA. Each person in the world is individualized from other people by a very small portion of DNA. These differences are how analysts are able to compare DNA samples in genetic testing. When genetic testing is being done, multiple areas of the DNA are examined by the analysts. There are four types of genetic testing: polymerase chain reaction analysis, short tandem repeat analysis, Y-chromosome analysis and mitochondrial DNA analysis.
Extraction
After the DNA sample is collected, the actual genetic material is extracted and examined. The extracted DNA is measured for quantity. Polymerase chain reaction is then used to copy certain areas of the DNA. Polymerase chain reaction allows for copies of the DNA segments to be made so that the DNA analyst can look at smaller pieces of the DNA.
Separation
After the DNA has gone through polymerase chain reaction, the individual sections are separated from one another through either slab gel or capillary electrophoresis. This is done so that the analyst knows which short tandem repeat (STR) region is being examined. The STR region is a shorter version of the variable number of tandem repeats, or VNTR. The lengths of the VNTR are what changes between individual people. The separated sections are then sample genotyped, which is where the repeats within the STR region are counted. The genotyping tells the analyst how the STR regions are different from that of another person's DNA.
Comparison
The result of the steps above is the sample's DNA profile. The DNA profile is then compared to another profile, such as that of a possible father in paternity testing or to a suspect in a crime. A matching profile is an "inclusion" while a profile that is not a match is an "exclusion." If testing for a genetic disease, the analyst would search the profile for the presence of the gene which causes the specific disease.
Tags: chain reaction, genetic testing, polymerase chain reaction, short tandem, short tandem repeat, tandem repeat
