Scientist loading agarose gel to separate DNA fragments, Great Ormond Street Hospital, London, May 2000. Scientists use a technique called gel electrophoresis to sort DNA into size order. During gel electrophoresis, an electric field pulls the pieces of DNA through a jelly-like slab: a gel. Smaller pieces move through the gel quicker and travel further than larger pieces. Scientists treat the sorted DNA pieces with a chemical that makes them show up under ultraviolet light.
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