Question

Ratan was a known sportsman in his school. While returning home he found some unknown miscreants beating a young fellow. He tried to drive them but by that time the fellow of injury. The police arrested Ratan and he was put on trial. The judge being convinced by Ratan‘ plea, ordered for DNA finger printing reports.

a) Ratan‘ fingerprints on the *** body were sufficient to convict him but the judge asked for authentic proof? What values can be observed?

b) What is the basis of DNA finger printing?

c) Explain the steps in DNA finger printing.

Answer 1

a) The judge showed wisdom and intention to search for the truth.

b)

1. DNA fingerprinting involves identifying differences in some specific regions in DNA sequence called as repetitive DNA.

2. Depending on base composition (A: T rich or G:C rich), length of segment, and number of repetitive units, the satellite DNA is classified into many categories,(Micro-satellites, mini-satellites etc).

3. These sequences normally do not code for any proteins, but they form a large portion of human genome. These sequence show high degree of polymorphism and form the basis of DNA fingerprinting.

c)

(i) isolation of DNA,

(ii) digestion of DNA by restriction endonucleases,

(iii) separation of DNA fragments by electrophoresis,

(iv) transferring (blotting) of separated DNA fragments to synthetic membranes, such as nitrocellulose or nylon,

(v) hybridisation using labelled VNTR probe, and

(vi) detection of hybridised DNA fragments by autoradiography.