Which of the following is not a feature of DNA fingerprinting?

The correct answer is Option (1) → Digestion of DNA by ligases.

DNA fingerprinting, as first developed by Alec Jeffreys, used Southern blot hybridisation with a radiolabelled VNTR (Variable Number of Tandem Repeats) probe. Its steps are isolation of DNA, digestion of DNA by restriction endonucleases, separation of the fragments by electrophoresis, blotting onto a membrane, hybridisation with the VNTR probe and detection by autoradiography.

Option (1) Digestion of DNA by ligases. — An incorrect statement. DNA is cut by restriction endonucleases, not by ligases. DNA ligase joins pieces of DNA; it cannot digest DNA, so this is not a step of the technique.

Option (2) Separation of DNA fragments by electrophoresis. — A correct statement. Electrophoresis separates the cut DNA fragments according to size. This is the third step of the technique.

Option (3) Hybridisation using labelled VNTR probe. — A correct statement. The blotted fragments are hybridised with a labelled VNTR probe, a satellite DNA that shows a very high degree of polymorphism. This is a true step.

Option (4) Detection of hybridised DNA fragments by autoradiography. — A correct statement. Autoradiography detects the fragments that have bound the radiolabelled probe and gives the band pattern. This is the last step.

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.”