GENETIC FINGERPRINTING

Genetic fingerprinting technique allows the identification of individuals from the lengths of their DNA fragments after samples of their DNAs have been treated with restriction nucleases. This technique has been very effective in resolving the pedigree and/or parentage issues and as diagnostic tool in crime detection.

The DNA samples can be obtained from traces of blood, hair or semen or any other body fluid. The human genome has Hypervariable regions of various lengths that varies from individual to individual. These hypervariable regions contain short sequences of DNA (e.g. GGAGGTGGGCAGGAG) called minisatellites that are repeated many times over. Individual differences in the lengths of restriction fragments appear to depend on, in part, on the number of times each minisatellite is repeated within the hypervariable region.

Using the genetic probes, the DNA fragments from the hypervariable region are separated by electrophoresis and radio-labeled to produce a genetic fingerprint. A completed finger print consist of many parallel bars unique to each individual. The genetic finger print of a child seems to be derived from it’s father or mother. Therefore this method is used to establish true blood relationships in cases of disputed parentage.

 

Diagrammatic representation of DNA molecule

DNA Finger printing

DNA fingerprinting was developed in1984 by Alec. J. Jeffrey at the University of Leicester. He was studying the myoglobin gene. The chemical structure of everyone's DNA is the same. And the only difference between people (or any animal) is the order of the Base pair.The information contained in DNA is determined primarily by the sequence of letters along the zipper. Using these sequences, every person could be identified solely by the sequence of their base pairs
As there are so many millions of base pairs, the task would be very time-consuming so the scientists are able to use a shorter method, because of repeating patterns in DNA. These patterns do not, however, give an individual "fingerprint, they are able to determine whether two DNA samples are from the same person, related people, or non-related people. DNA finger printing can also be done, by using VNTRs. On some human chromosomes, a short sequence of DNA has been repeated a number of times which may vary from one to thirty repeats. These repeat regions are usually bounded by specific restriction enzyme sites so we can cut out the segment of the chromosome containing this variable number of tandem repeats (VNTR's ) and then identify the VNTR's for the DNA sequence of the repeat. To make DNA finger print in the laboratory, following steps are necessary:

- Isolation of DNA.

- Cutting, sizing, and sorting using special enzymes called restriction enzymes to cut the DNA at specific places.

- Transfer of DNA to nylon by distributing the DNA pieces by placing the sheet on the gel and soaking them overnight.

- Probing which involves adding radioactive or colored probes to the nylon sheet which produces a pattern called the DNA fingerprint.

-The final DNA fingerprint is built by using several probes (5-10 or more) simultaneously.

Practical Applications of DNA Fingerprinting

-Paternity and Maternity

As the person inherits his or her VNTRs from his or her parents, Parent-child VNTR pattern analysis has been used to solve standard father-identification cases. In 2002 the famous actress, Elizabeth Hurley used DNA profiling to prove that Steve Bing was the father
of her child Damien.

-Criminal Identification and Forensics

DNA isolated from blood, hair, skin cells, or other genetic evidence left at the scene of a crime can be compared .FBI and police labs around the U.S. have begun to use DNA fingerprints to link suspects
to biological evidence – blood or semen stains, hair, or items of clothing. It was Colin Pitchfork who was the first criminal caught based on DNA fingerprinting evidence. He was arrested in 1986 for the rape and murder of two girls and was sentenced in 1988. Another high profile case is of O.J. Simpson was cleared of a double murder charge in 1994 which relied heavily on DNA evidence.

-Personal Identification

The notion of using DNA fingerprints as a sort of genetic bar code to identify individuals is already under discussion.

-Diagnosis of Inherited Disorders

To diagnose inherited disorders in both prenatal and newborn babies.
These disorders may include cystic fibrosis, hemophilia, Huntington's disease, familial Alzheimer's, sickle cell anemia, thalassemia, and many others.

-Developing Cures for Inherited Disorders

By studying the DNA fingerprints of relatives who have a history of some particular disorder one can identify DNA patterns associated with the disease.

-Identification of Chinese medicine

The Hong Kong Baptist University was able to use DNA fingerprinting to identify the Chinese medicine—Lingzhi in 2000 .

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