Scientist setting up a Southern blot, Great Ormond Street Hospital, London, May 2000. If DNA is extracted from blood and cut up using enzymes, the result is a mixture of about 1.5 million DNA pieces of different lengths. Scientists can separate this mixture on a gel. To look at a particular piece of DNA, they first have to transfer it from the wobbly gel to a tough nylon membrane. This technique is called 'Southern blotting' after its inventor, biologist Ed Southern.
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