JAMES KING-HOLMES / SCIENCE PHOTO LIBRARY JAMES KING-HOLMES / SCIENCE PHOTO LIBRARY
A researcher marks samples of DNA with a radioactive tag in preparation for sequencing. During electrophoresis the DNA fragments move along the gel, separating according to size. The DNA banding pattern, which will be unique to the individual under study, can then be revealed by applying radiographic film to the gel so that the radioactive markers produce a trace. The result is known as a DNA sequencing autoradiogram. Sequencing involves mapping the base-pair sequence of DNA- this is done most usefully to those sections of DNA called genes which encode specific proteins.
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