Scientist pipetting a DNA reaction solution.
© Science Museum / Science & Society Picture Library
Scientist pipetting a DNA reaction solution containing blue dye prior to loading a gel, 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.