Forensic scientists use DNA to analyse a wide variety of different samples.
All of these can be DNA profiled and compared to reference samples:
- hairs or saliva left on a balaclava worn during a robbery
- semen located at a rape scene
- blood collected from an assault
- skin cells on clothing
- traces of assailant's skin or blood under a victim's fingernails.
DNA is unique in all individuals except identical twins.
Forensic analysis of DNA involves testing specific areas of an individual's DNA, areas that have been identified by scientists as being 'polymorphic'. This means that these regions tend to be different from one person to the next. A collection of results from these polymorphic areas for one person is referred to as a DNA profile for that person.
By comparing the DNA profile obtained from a crime sample with that prepared from an individual's reference sample (usually blood or a mouth swab), the individual concerned can be included or excluded as a possible source of the crime sample.