It is very difficult to avoid leaving your DNA behind. Whether you cough, sneeze, talk or just touch someone or something, you will leave a trace of your DNA wherever you go.

 

What actually is it?
DNA stands for Deoxyribonucleic Acid. It is a molecule found in the cells of all people, animals, plants and other organic matter. These cells are the building blocks of any living organism, of which the human body has countless millions.

DNA carries the genetic code that makes each of us unique. Variations in the code are responsible for physical differences between individuals, such as height, sex, hair and eye colour etc.

Half of our DNA has been inherited by each parent. You can inherit different mixes of DNA which is why brothers and sisters are not identical but identical twins have developed from the same genetic code and have identical DNA. Children within one family are more likely to have similar DNA than unrelated individuals.

DNA exists as an invisibly thin strand in a tangled knot in the cells of the body. If straightened out, the DNA from each cell would be two metres long. That is more than six feet of it inside a cell invisible to the human eye! The DNA from all the cells in the human body would stretch to the sun and back 500 times. That is more than 45,000,000,000 miles of DNA!

 

Why is it important in policing and solving crime?
A DNA sample found at the scene of a crime can be used in the following ways:

• To compare with a sample taken from a suspect. If there is a match, it can be used as evidence in court.
• To match to samples taken from other crime scenes which can then be linked together, revealing a series of offences.
• To search against other DNA profiles from scenes of unsolved crime.
• To eliminate a suspect.
• To identify offenders through close relatives.
• To identify deceased persons.

 

How is it used?
To obtain a DNA sample from a person in police custody the arresting officer uses a small mouth swab (also known as a buccal swab). They gently rub the swab on the inside of the cheek; collecting mouth cells from which the DNA can then be analysed.

The technology of DNA profiling doesn't yet allow the examination of every single difference between people's DNA. However, techniques used look at specific areas of nuclear DNA which are known to vary widely between people.

These areas vary in length between different people's DNA. DNA 'profiling' analysis and measures these differences in length and by comparing these profiles it is then possible to link a person with DNA from a crime scene or weapon.

The National DNA Database is used by all forces to compare samples recovered form crime scenes with the number of subject profiles retained on the NDNAD at over five million.

If DNA is only present in very small amounts it can be greatly amplified using a special technique called Polymerisation Chain Reaction or PCR for short. PCR can produce a result from just one nanogram (one thousand millionth of a gram) of DNA.

Profiling takes between 16 and 24 hours in the laboratory depending on the sample.

From crime scene to database to name of a possible suspect can be achieved within 48 hours.