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. Most exclusions are obvious. If not so obvious, the bands are measured through the computer. Determining a match.