There would be a DNA sample from several people, each sample in a different hole.
The gel is made from something called agarose (derived from seaweed) and is just a pure firm jelly.
Small fragments move faster than larger fragments, so the DNA fragments are separated as they move in the gel. The gel is checked by shining ultraviolet light on it to check for a nice strong DNA smear (see bottom picture on the next page).
In the gel there is a chemical called “ethidium bromide” which sticks to all DNA fragments and allows the DNA to be seen when an ultraviolet light is shone on it.
Most of the method I have described is quite routine in the lab since the late 1970s and not developed by Alec but by Ed Southern at Oxford (hence “Southern blotting”).
Alec’s particular contribution was the choice of the “probe”.At this stage, the DNA can be seen as a smear in the gel rather than the “lots of bands” that is characteristic of DNA fingerprints – that is what comes later.A gel (similar to one Alec would have used, for DNA fingerprinting, they are larger but essentially the same).Some letters code for proteins, which then do stuff in the cell (like making the cell move or speeding up chemical reactions).Other letters do nothing at all and are just “spacer” or “junk” DNA.We add a blue dye to the DNA fragments using a pipette, and use a pipette to move the blue DNA liquid from a colourless tube into the “well” – little hole – in the gel (see the top picture on the next page).We use a blue dye to see where we have added the DNA on the gel – it’s just for our benefit so we don’t add two different DNA samples in the same hole!Technical improvements, including a number of additional DNA probes and various DNA fragment detection methods, have since been published.With the recent advent of the PCR technique (Polymerase Chain Reaction) and PCR-based methods like RAPD (Random Amplified Polymorphic DNA), DNA fingerprinting has widened its applicability and attracted a growing number of scientists.The gel is placed in a colourless liquid and electrodes are attached to the gel equipment, and a power supply is turned on.By putting the liquid DNA fragments in the hole at one end and passing an electric current through the gel, the DNA fragments move into the gel with the electric current.