DNA FAQs
Q:What is DNA?
A: DNA stands for Deoxyribonucleic Acid. DNA is the genetic material found in the nucleus (centre) of every living cell in your body and contains all your genetic information - it is a genetic ‘code' unique to each of us with the exception of identical twins. We inherit 50% of our DNA from our mother and 50% from our father. Our DNA determines the colour of our eyes, our hair colour, even our height. The DNA in a person's body is the same regardless of which body fluid or cell type it comes from.
Q: What is it used for?
A: In forensic science the process of analysing DNA is referred to as DNA profiling. This technology makes it possible to compare a DNA profile from a person, known as a reference sample, with a DNA profile from an evidence crime sample. If there is a match between the DNA profile from the person and that of the crime sample then the probability of finding this match if the DNA did not come from that person is 1 in more than 1 billion. This why DNA has become so important in criminal investigations and can be used to help prove either the innocence or guilt of suspects.
Q: How reliable is DNA?
A: DNA is very reliable because it doesn't change during our lifetime. It is very easy to say that biological evidence does not come from someone if the DNA profiles are different. If there is a match between the DNA profile from the person and that of the crime sample then the probability of finding this match if the DNA did not come from that person is 1 in more than 1 billion.
Q: What is CJ analysis?
A: When a suspect is arrested the police have the right to take a DNA sample, usually a mouth swab. This is known as a criminal justice (CJ) sample. All samples are analysed and the profiles stored on the Scottish database as well as being sent to the National DNA Database.
Q: What is the National DNA Database?
A: The database is a collection of all the DNA profiles from people who have been arrested in England, Wales and Scotland as well as unidentified DNA profiles from crime scenes. The database was set up in 1995 and is based in Birmingham. When the profiles from Crime Scenes are compared with the profiles from the all people on the database and a match is found, the police are told. This allows the police to obtain a new sample from the person suggested and the forensic scientist can compare the new sample against the crime scene sample. If there is a match the person can be linked to previous crimes and this evidence may then be used in court.