DNA (deoxyribonucleic acid) is the genetic blueprint that determines our biological characteristics. DNA is a long molecule located in almost every cell in the human body. When we are conceived, we inherit half of our DNA from our mother and half from our father. Although every human’s DNA is 99.9% identical, the remaining 0.1% is enough to uniquely identify an individual. Our DNA is made up of about 3 billion base pairs, the building blocks of DNA composed mainly of carbon and sugar. The 0.1% (3 million) base pairs that make us unique are what constitute our DNA fingerprint.
Over the past 20 years, courts have been able to rely upon the consistent accuracy of DNA profiling, also known as DNA fingerprinting, to solve crimes. DNA profiling has even been used to solve crimes that are more than 30 years old.
Here’s how DNA profiling is done:
- Specimens are collected from the crime scene. Anything can be used to extract DNA: Hair, blood, bodily fluids, etc. In some cases, victims may have scratched their attackers, in which case skin cells can be extracted from underneath the victim’s fingernails in order to identify the criminal
- The DNA needs to be isolated and cut so that it can be matched against other samples. Special enzymes recognize patterns in the DNA and cut the strand
- In a process called electrophoresis, the strands are then placed on a gel where they are separated an electric current passed through it.
- The resulting fragments are compared against samples of all suspects and a match is determined.DNA profiling is mostly used in sexual offences (60%), homicide (20%), assaults (7%), robbery (7%), criminal damage (1%), and other cases (5%).
DNA profiling narrows the list of suspects that authorities need to work through. The FBI commented that DNA profiling allows them to dismiss one-third of rape suspects because the DNA samples do not match. Authorities recognize the possibility of specimens being planted at crime scenes, and therefore continue to investigate the crime based on motive, weapon, testimony, and other clues in order to more accurately solve the case.