DNA fingerprinting

DNA fingerprinting is a laboratory technique used to determine the probable identity of a person based on the nucleotide sequences of certain regions of the human DNA that are unique to individuals.
The father of DNA fingerprinting
DNA profiling was first developed by British geneticist Sir Alec John Jeffreys at the University of Leicester in 1985. Considered the father of DNA fingerprinting he shaped the field of forensic DNA.
The nucleic acid hybridisation
technique
In DNA fingerprinting, DNA molecules are identified by a modern technique called Southern blotting (Southern blot hybridisation) which was first developed by E.M. Southern in 1975.
Southern blotting is a nucleic acid hybridisation technique used to identify DNA fragments with the help of a DNA probe. The DNA probe is a radioactively or
fluorescently labelled single-stranded DNA (SSRDNA). In the technique of
Southern blotting, radio labelled VNTR (VARIABLE number of Tandem Repeats)
is used as the DNA probe.
How the technique works
1. Electrophoresis and
separating the double strands
A complete DNA molecule is isolated from any part of the body such as a hair root or a drop of blood or semen. This isolated DNA is subjected to the action of restriction endonuclease enzyme (an enzyme that cuts a DNA molecule at a particular place). As a result, the DNA molecule becomes fragmented. The DNA fragments are then subjected to gel electrophoresis (a laboratory
technique used to separate DNA, RNA or protein molecules based on their size and electrical charge). During this process, the double-stranded DNA fragments (ds DNA) migrate in the gel and become separated. The double-stranded DNA fragments separated by electrophoresis are now treated with alkali (NaOH solution). The double- stranded DNA fragments (ds DNA) now become single-
stranded (ss DNA) and denatured.

2. Blotting on filter paper
The single-stranded denature d DNA fragments are then transferred to a synthetic membrane-like nitrocellulose filter paper or nylon filter paper by
blotting and then baked at 80oC for 2 hours. During this process, the single-
stranded DNA fragments get fixed permanently on the filter. This process is called blotting.
3. Binding
The nitro cellulose filter or nylon filter is now placed in a solution of artificially synthesised, radio-actively labelled, denatured, single-stranded DNA (ss DNA)
called DNA probe. Special DNA probes are made in the laboratory. These DNA probes contain repeated sequences of bases complementary to those on VNTRS.
These probes are made radio-labelled with radio-active isotopes. The radio-
labelled DNA probe binds to the complementary denatured single-stranded
DNA in the filter. Thus, the DNA probe hybridises with the DNA fragments on the filter to from DNA-DNA hybrid.
4. X-raying of the hybrid DNA
The filter paper is washed to remove unbound DNA probes from the filter. It is then photographed on to an X-ray film by autoradiography. Dark bands develop at the probe sites. The X-ray image of the hybrid DNA is called DNA fragments. This DNA fingerprint can be analysed and identified.
Legal validity of DNA fingerprinting
1. The law under the Section 53 of the Code of Criminal Procedure (CrPC )
empowers criminal courts to use reasonable necessary force to conduct forensic examination
2. DNA analysis is of utmost importance in determining the paternity of a child in the case of civil disputes. The need for this evidence is most significant in criminal cases, civil cases and in the maintenance proceedings in criminal courts under Section 125 of the CrPC.
Applications
DNA testing with an accuracy rate of 99.9% is used to establish paternity and parentage, to identify victims of war and large scale disaster, to study biodiversity of species, to track genetically modified crops, and to settle immigration disputes.
In short, our DNA is the greatest history and crime thriller book ever written.