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The Section of Forensic Genetics analyses trace evidence obtained by the police at the crime scene. Trace evidence may originate from homicides, assaults, rapes, burglaries, etc. The police send us this trace evidence and we ascertain its nature and DNA content. Examples of biological trace evidence include blood, semen, hair, saliva, scrapings from beneath fingernails, etc. The trace evidence we analyse is often obtained from articles of clothing, weapons or objects found by police technicians at or near the crime scene. It is secured by swabbing the object concerned and submitting the swab to our laboratories for analysis.
The police use DNA recovered from the crime scene as part of their investigations. A suspect may be required to provide a saliva or blood sample. This can be analysed and compared to DNA from the crime scene, serving as a ‘genetic fingerprint’.
We start by extracting the DNA from the cells in which it is located. The biochemical methods we use for this purpose depend on the nature, volume and state of the material we have received. We then determine the amount of DNA present in the sample and if there is enough we perform the analysis yielding the DNA-profile.
As a matter of routine we analyse sixteen particular areas of DNA that vary from person to person. We always test samples twice to see whether we can duplicate the result of the first test. Doing so minimises the possibilities of error.