Arrange the following steps involved in the DNA fingerprinting in correct sequence.
A. Gel electrophoresis
B. Autoradiography
C. Isolation of DNA
D. Blotting
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → C, A, D, B
DNA fingerprinting finds the pattern of VNTRs (variable number tandem repeats) in a person’s DNA. It follows the steps of the Southern blot technique.
(C) Isolation of DNA — this comes first. The DNA must be taken out of the cells before anything else is done. The DNA is then cut with restriction endonucleases.
(A) Gel electrophoresis — this comes second. The cut pieces are separated by size in a gel.
(D) Blotting — this comes third. The separated fragments are transferred from the gel to a nitrocellulose or nylon membrane. Then they are hybridised with a labelled VNTR probe.
(B) Autoradiography — this comes last. The hybridised fragments are detected on X-ray film, because the probe is radioactive.
NCERT Extract:
DNA Fingerprinting – “… The technique, as used earlier, involved Southern blot hybridisation using radiolabelled VNTR as a probe. It included
(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.”