Introduction
DNA testing is a common procedure used to identify individuals based off of what is present in their DNA code. Although 99.9 percent of DNA is shared between all human beings, the remaining 0.1 percent is what makes us individual from one another. The only two individuals who share the exact same DNA sequence are identical twins. Discovering the difference between this tenth of a percent, is what DNA testing is all about. DNA testing is an important part of many fields of science especially disease research, criminal forensics and paternity testing.
DNA (deoxyribonucleic acid) are nucelic acids that give instructions on how our bodies look and operate. For example, your DNA decides what color your hair and eyes will be, how tall you will grow, even the features of your face. Each cell in your body contains a complete sample of what your DNA looks like.
Obtaining a Sample
DNA can be found in many places on and in the body. DNA samples can come from blood, semen, hair, skin tissue, cheek swabs and amniotic fluid. How a DNA sample is obtained depends on the situation. For paternity and genetic testing, samples can be gained through amniocentesis, chorionic villus sampling (CVS), or by pricking the heel of the baby and drawing a blood sample. In forensic testing samples are usually given through cheek swabs, or samples may be taken at the crime scene from evidence. Once a sample has been taken, there are two main types of actual testing, RLFP and PCR.
RLFP
Restriction fragment length polymorphism (RFLP) is the most accurate form of DNA testing, but also takes the longest to perform. RFLP is performed by lab technicians and involves comparing specific sections of DNA between two samples, and looking for similar base pairs. Since most human DNA is shared, lab scientists look at sections that have a higher probability of being unique to each person. If two base pairs are a match, the scientist can say with almost complete certainty that the DNA belongs to the same person (or in the case of paternity, that the father and child's DNA show a relationship). RFLP DNA testing is not always an available option. RFLP requires recent and large samples.
PCR
Polymerase chain reaction (PCR) DNA tests come into play when RFLP cannot be used. With a PCR test, even if the DNA sample is old (such as an old blood stain), the PCR can still determine a match. The match is not as accurate as an RLFP test. Instead of looking at entire sequences of base pairs, PCR tests look for one specific gene match, most commonly the HLA DQ alpha gene. This is done by copying the available DNA. DNA copying takes small fragments of DNA and multiplies them into millions of copies. This slowly reveals a DNA profile of the person the DNA belongs to, which can then be compared to another sample for matching.
