Molecular geneticist labelling a radioactive probe, Great Ormond Street Hospital, London, May 2000. Scientists can pick out a particular piece of DNA using a DNA probe. The average DNA probe is about 1000 letters long. Scientists tag the probe with either a chemical dye or radioactivity so they can see it. They then heat it so that it unzips into two separate strands. Finally it is washed over by a nylon membrane. The unzipped DNA probe sticks to any matching pieces of DNA on the membrane by a proces called DNA hybridisation.
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