JAMES KING-HOLMES / SCIENCE PHOTO LIBRARY JAMES KING-HOLMES / SCIENCE PHOTO LIBRARY
Southern blotting. A researcher transfers an electrophoresis gel containing DNA into a tray of salt solution prior to blotting the DNA onto nitrocellulose paper. The purple dye shows how far electrophoresis has progressed. Southern blotting is a technique to reveal specific fragments of DNA (deoxyribonucleic acid) in a complex mixture. The total DNA is cut into fragments and separated according to size by gel electrophoresis. The DNA is then blotted onto a sheet of nitrocellulose placed on top, and a radioactive DNA probe added to the nitrocellulose. The resulting banding pattern, revealed by autoradiography, can be used to map the structure of particular genes.
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