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Sorting it out

Scientists use a technique called gel electrophoresis to sort out pieces of DNA in order of their size. During gel electrophoresis, an electric field pulls the pieces of DNA through a jelly-like slab: a gel. Smaller pieces move through the gel more quickly and so travel further than larger pieces. Scientists then treat the sorted DNA pieces with a chemical that makes them show up under ultraviolet light.

DNA fragments on a gel.
DNA fragments on a gel.
National Medical Slide Bank/Wellcome Photo Library

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