GEOFF TOMPKINSON / SCIENCE PHOTO LIBRARY GEOFF TOMPKINSON / SCIENCE PHOTO LIBRARY
Scientists examining DNA sequences. Scientists study DNA autoradiograms and photos of ethidium bromide stained gels. These are ways of visualising a DNA sequence made by an electrophoresis gel. In autoradiography, the DNA fragments are labelled with a radioactive isotope. When they have been separated by electrophoresis, DNA fragments in the gel are placed on a sheet of X-ray film. The more fragments in a given location, the darker the spot produced on the film. Ethidium bromide may also be used to stain a gel; the result is a gel in which the fragments fluoresce under UV light and may be photographed.
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