DNA Fingerprinting NEET MCQ - NEET Practice Questions & Answers

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DNA Fingerprinting

As we have figured out from the HGP, 99.9 % of the base sequence among humans is the same.
It is that difference in the sequence of DNA which makes every individual unique in their phenotypic appearance.
DNA fingerprinting is a very quick way to compare the DNA sequences of any two individuals.
DNA fingerprinting involves identifying differences in some specific regions in DNA sequence called repetitive DNA because, in these sequences, a small stretch of DNA is repeated many times.
These repetitive DNA are separated from bulk genomic DNA as different peaks during density gradient centrifugation.
The bulk DNA forms a major peak and the other small peaks are referred to as satellite DNA.
Depending on the base composition (A: T rich or G:C rich), length of the segment, and a number of repetitive units, the satellite DNA is classified into many categories such as micro-satellites, mini-satellites etc.
These sequences normally do not code for any proteins, but they form a large portion of the human genome.
These sequences show a high degree of polymorphism and form the basis of DNA fingerprinting.
Since DNA from every tissue (such as blood, hair follicle, skin, bone, saliva, sperm etc.), from an individual showing the same degree of polymorphism, they become a very useful identification tool in forensic applications.
Further, as the polymorphisms are inheritable from parents to children, DNA fingerprinting is the basis of paternity testing, in case of disputes.
The technique of DNA Fingerprinting was initially developed by Alec Jeffreys.
He used satellite DNA as a probe that shows a very high degree of polymorphism. It was called the Variable Number of Tandem Repeats (VNTR).
The VNTR belongs to a class of satellite DNA referred to as mini-satellite.
A small DNA sequence is arranged tandemly in many copy numbers.
The copy number varies from chromosome to chromosome in an individual.
The numbers of repetition show a very high degree of polymorphism.
As a result, the size of VNTR varies in size from 0.1 to 20 kb.
Consequently, after hybridisation with VNTR probe, the autoradiogram gives many bands of differing sizes.
These bands give a characteristic pattern for an individual DNA
The technique, as used earlier, involved Southern blot hybridisation using radiolabeled VNTR as a probe.
It included:
- isolation of DNA,
- digestion of DNA by restriction endonucleases,
- separation of DNA fragments by electrophoresis,
- transferring (blotting) of separated DNA fragments to synthetic membranes, such as nitrocellulose or nylon,
- hybridisation using labelled VNTR probe, and
- detection of hybridised DNA fragments by autoradiography.