The DNA is obtained from the sample by centrifugation. The next step is to cut up the DNA strands using a “restriction enzyme”. The gel is like a sieve, in that it separates the different sizes of DNA fragment generated by cutting up the DNA.
The gel-separated DNA fragments are then transferred to white nitrocellulose paper, so the paper now carries an exact replica of the DNA on the gel. This is called “Southern blotting”. The next step is hybridisation using labelled VNTR probe, and detection of hybridised DNA fragments by autoradiography.