What is DNA?

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. It is therefore possible to create a DNA profile from samples such as blood, saliva, semen, hair roots etc. 

The importance of DNA

In Forensic Science the process of analysing DNA is referred to as DNA profiling and involves targeting 10 specific parts within the DNA known as Short Tandem Repeats (STRs). 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.

DNA was first used in criminal analysis in the UK in the 1980's following a double rape and murder in Leicestershire.  This led to the production of the first DNA profile which showed that both murders had been carried out by the same individual, who was not the prime suspect.  Leicestershire Constabulary then carried out the world's first DNA intelligence-led screening. All adult males in three villages - a total of 5,000 men - were asked to volunteer and provide blood or saliva samples. A local baker, Colin Pitchfork was arrested and his DNA profile matched with the semen from both murders. In 1988 he was sentenced to life for the two murders.

The Scottish DNA Database

The Scottish DNA Database is held in Dundee.  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, set up in 1995 and based in Birmingham.

Working in DNA

The DNA sections of SPA provide four key services to the Scottish police forces and law enforcement agencies:

1. Casework - These are cases where there is a known accused and comparisons can be made between reference samples and crime sample evidence material.

2. Undetected cases -These are cases where the Police do not have a suspect and where the Scottish DNA database is utilised to identify matches between a crime sample DNA profile and a person held on the database.

3. Criminal Paternity testing - rapes, incest

4. Body identification

Investigating cases

DNA profiling is used in solving all crime types ranging from volume crime such as housebreaking and car crime to serious crimes like assaults, murder and rape. The forensic scientists will look for suitable samples at a crime scene, examining such items as weapons, clothing, and hair anything at all from which they can obtain a body fluid.

Scottish DNA Database

The DNA database can help to solve undetected cases where there is no suspect.

Paternity testing

DNA profiling processes can be used to determine whether a child's father is the real father.  In cases of familial rape or incest we have to first prove that the child is in fact the daughter or it can be used to prove if a child has been conceived as a result of a rape.

The SPA does carry out civil paternity DNA processing requests on behalf of the legal profession. If you are a lawyer and need this service, please email: spafsdnadatabase@spa.pnn.police.uk or telephone 01382 315950.

Body identification

DNA profiling can be used to formally identify a body. This is achieved by obtaining DNA profiles from both the mother and father or by relating personal effects to a body.  DNA profiling is used in such cases after all other means of identifying a body have been carried out.