DNA typing has been used at the Vermont Forensic Laboratory since 1991. The methods have changed over the years, but the basic idea remains the same. Deoxyribonucleic acid (DNA) is found in every cell of the body except mature red blood cells. DNA is made up of double-stranded molecules inherited from your parents and is the molecular code from which your body is built.
The DNA analysts at the laboratory make use of non-coding areas of DNA called short tandem repeats (STRs) to differentiate the DNA of one individual from that of another individual (except for identical siblings). There is considerable variation in the number of repeat units that may be contained at a particular location (or locus) of DNA. Since each individual has two copies of each DNA location, one inherited from each parent, the actual combination of types across the 23 locations examined provides distinguishable profiles for each individual. Currently the lab uses a method called the polymerase chain reaction (PCR) to make many copies of small amounts of DNA so that they can be typed. The typing results are called a DNA profile.