DNA fingerprinting

Last reviewed 01/2018

This technique involves the use of restriction fragment length polymorphisms (RFLP): fragments of DNA of differing molecular mass between individuals resulting from digestion of the genome by restriction enzymes. This DNA may be isolated from a forensic specimen and from the blood of a suspect.

A specific restriction enzyme digests the DNA at sites that differ in length because they have variable numbers of randomly repeated units termed hypervariable regions. Hypervariable regions show a great deal of variability - polymorphism - between individuals. Using the appropriate DNA probe for the fragments, the correspondence in position between the hypervariable region blot analyses from the suspect's sample and the forensic specimen provides an indication of the extent to which they are related.

The chance that there will be a match from two specimens that are not from the same individual range from 1 in 100,000 to 1 in 1 million (1). A non-match between two specimens means that they cannot come from the same person.

There is a concern that the chances of a match of two specimens from two different people may be higher in specific subgroups within a population or even with a family, than in the general population.

Reference:

• Housman DE (1995). DNA on trial - the molecular basis of DNA fingerprinting. NEJM, 332, 534-5.