NEET Botany Molecular Basis of Inheritance Questions Solved

BOARD

In a maternity clinic , for some reasons the authorities are not able to hand over the two new-borns to their respective real parents. Name and describe the technique that you would suggest to sort out the matter.

Technique: DNA fingerprinting may be used to sort out the matter. It works on the principle of polymorphism in DNA sequences. DNA from every tissue ( such as blood, hair-follicle, skin, bone, etc.) from an individual show the same degree of polymorphism, hence become very useful indentification tools in forensic applications. As polymorphisms are inheritable from parents to children, DNA fingerprinting forms the basis of paternity testing, in case of confusion and disputes.

Procedures:

1. DNA molecules are isolated from a sample of blood, semen or other body fluid or tissue by using specific techniques such as high speed refrigerated centrifuge.

2. If DNA is in poor condition, or available only in minute quantities the particular DNA may be amplified by making many copies of it with the help of using PCR.

3. DNA molecules are cleaned i.e. cut into fragments at specific sites with the help of a site recognizing restriction endonuclease enzyme for the purpose of restriction fragment length analysis. The DNA fragments contain VNTRs ( Variable Number Tandem Repeats).

4. DNA fragments are then sorted out according to length on an agarose gel slab by the technique called electrophoresis.

5. Double stranded DNA is now split into single strands by using alkaline chemicals.

6. The islolated DNA fragments in the gel are copied onto a nylon nitrocellulose sheet placed on gel. This technique is called Southern Blotting.

7. Special DNA probes are prepared in lab. These contain repeated sequences of nucleotides complementary to those on VNTRs. The probes are made radioactive . The radioactive DNA probes bind to repeat sequences on the nylon sheet. This is called hybridization . An X-ray film is exposed to nylon sheet to mark the places where radioactive DNA probes have bound to DNA fragment. These places are marked as dark bands when X-ray film is developed. This process is called auto radiography.

8. The dark bands on X-ray film represent the DNA fingerprints.

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