Once extracted, it's put in another small tube and the DNA is cleansed with organic solvents. Particular enzymes can cut the DNA molecule at specific sites of its sequence. This process separates fragments according to their lengths. At the other end, positively charged electrical currents flow. That causes DNA fragments to move toward it across the gel.
Shorter fragments move faster and farther.
Southern transfer or blotting. In order to have a permanent copy of the fragments, a sheet of nylon is placed on top of the gel. Paper absorbs the liquid in the gel so the fragments attach themselves to the nylon sheet. At the same time, the DNA is treated with chemicals or heat to cause the fragments to unzip into two single strands. Interpreting the DNA print.