DNA profiling Technique

DNA profiling is a technique employed by forensic scientists to assist in the identification of individuals on the basis of their respective DNA profiles. It is also called DNA testing, DNA typing, or genetic fingerprinting.

DNA profiles are encrypted sets of numbers that reflect a person’s DNA makeup, which can also be used as the person’s identifier. DNA profiling should not be confused with full genome sequencing.

Although 99.9% of human DNA sequences are the same in every person, enough of the DNA is different to distinguish one individual from another.DNA profiling uses repetitive (“repeat”) sequences that are highly variable, called variable number tandem repeats (VNTR). VNTRs loci are very similar between closely related humans, but so variable that unrelated individuals are extremely unlikely to have the same VNTRs.
The DNA profiling technique was first reported in 1985 by Sir Alec Jeffreys at the University of Leicester in England, and is now the basis of several national DNA databases.

DNA profiling process

The process begins with a sample of an individual’s DNA (typically called a “reference sample”). The most desirable method of collecting a reference sample is the use of a buccal swab, as this reduces the possibility of contamination. When this is not available (eg because a court order may be needed and not obtainable) other methods may need to be used to collect a sample of blood, saliva, semen, or other appropriate fluid or tissue from personal items (e.g. toothbrush, razor, etc) or from stored samples (e.g. banked sperm or biopsy tissue). Samples obtained from blood relatives (biological relative) can provide an indication of an individual’s profile, as could human remains which had been previously profiled.

A reference sample is then analyzed to create the individual’s DNA profile using one of a number of techniques, discussed below. The DNA profile is then compared against another sample to determine whether there is a genetic match.

RFLP analysis- Restriction Fragment Length Polymorphism


PCR analysis – Polymerase Chain Reaction


STR analysis – Short Tandem Repeats

The method of DNA profiling used today is based on PCR and uses short tandem repeats (STR). This method uses highly polymorphic regions that have short repeated sequences of DNA (the most common is 4 bases repeated, but there are other lengths in use, including 3 and 5 bases). Because different unrelated people have different numbers of repeat units, these regions of DNA can be used to discriminate between unrelated individuals. These STR loci (locations) are targeted with sequence-specific primers and are amplified using PCR. The DNA fragments that result are then separated and detected using electrophoresis. There are two common methods of separation and detection, capillary electrophoresis (CE) and gel electrophoresis.

AmpFLP Amplified Fragment Length Polymorphism


Y-chromosome analysis



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