Biology · Molecular Basis of Inheritance · NEET
The NCERT order is: (i) isolation of DNA, (ii) digestion of DNA by restriction endonucleases, (iii) separation of DNA fragments by electrophoresis, (iv) transferring (blotting) the fragments to a synthetic membrane, (v) hybridisation using a labelled VNTR probe, and (vi) detection of hybridised fragments by autoradiography. NEET loves this exact order, so memorise it as: Isolate, Digest, Electrophorese, Blot, Probe, Photo.
VNTR means Variable Number of Tandem Repeats. It is a short DNA sequence repeated many times, and the number of repeats is different in every person. This variation (polymorphism) is high, so the VNTR pattern acts like a unique barcode. A labelled VNTR probe binds to these repeat regions to reveal the pattern.
No. Zinc finger analysis is NOT used in DNA fingerprinting and is a common NEET trap. The real requirements are restriction enzymes, DNA-DNA hybridisation with a VNTR probe, and (in modern methods) PCR. A zinc finger is a protein motif that binds DNA, but it has no role in the fingerprinting technique.
The restriction endonuclease cuts the isolated DNA at specific sites into many small fragments. This is step (ii). Cutting is needed so that the fragments can then be separated by size using gel electrophoresis, which sorts them into a pattern that can be probed.
After electrophoresis, the separated DNA fragments are transferred (blotted) from the gel onto a synthetic membrane, such as nitrocellulose or nylon. This transfer of DNA is called Southern blotting, named after Edwin Southern. It keeps the fragments in the same pattern so the VNTR probe can bind them.
DNA fingerprinting was developed by Alec Jeffreys. In India, it was applied by Lalji Singh and V.K. Kashyap. The sensitivity of the technique is increased by using the Polymerase Chain Reaction (PCR), which amplifies tiny amounts of DNA so even a very small sample gives a clear result.
Arrange the following steps of DNA fingerprinting in the correct sequence. A. Isolation of DNA and its digestion by restriction endonucleases. B. Hybridisation using a labelled VNTR probe. C. Transferring of separated DNA fragments to synthetic membranes. D. Detection of hybridised DNA fragments by autoradiography. E. Separation of DNA fragments by electrophoresis.
Which of the following is not required for any of the techniques of DNA fingerprinting available at present?
DNA polymorphism forms the basis of:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is a lab method that finds the differences in repetitive DNA (VNTRs) between people. Because these repeat patterns are unique to each person (except identical twins), the technique can identify a person or check family relationships.
There are 6 steps: isolation of DNA, digestion by restriction endonucleases, separation by electrophoresis, blotting onto a membrane, hybridisation with a labelled VNTR probe, and detection by autoradiography.
It is used in forensic science (to identify criminals or victims), paternity and maternity testing, identifying family and evolutionary relationships, and studying genetic diversity in populations.
VNTRs show a very high degree of polymorphism, meaning the number of repeats varies greatly between individuals. This high variation makes each person's pattern nearly unique, so it works like a genetic barcode.
PCR (Polymerase Chain Reaction) amplifies (makes many copies of) DNA. It increases the sensitivity of the technique so that even a very small or old DNA sample can be analysed.
