What is Southern Blot

Southern blot is a method routinely used in molecular biology to check for the presence of a DNA sequence in a DNA sample. Southern blotting combines agarose gel electrophoresis for size separation of DNA with methods to transfer the size-separated DNA to a filter membrane for probe hybridization. The method is named after its inventor, the British biologist Edwin Southern.The southern blot is used to verify the presence or absence of a specific nucleotide sequence in the DNA from different sources and to identify the size of the restriction fragment that contains the sequence.
In this procedure, the DNA is isolated from each source and then digested with a specific restriction enzyme. The DNA restriction fragments are then loaded onto an agrose gel and the fragments separated by electrophoresis according to size, with the smaller fragments migrating faster than larger fragments. The DNA is then transferred from the fragile gel to a nylon filter.


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Next the radioactively labeled nucleic acid probe is added. The probe binds to complementary DNA segments. Note that the DNA segment being probed is not present in organism B
To detect the position of the radioactive probe, the nylon membrane is covered with an X-ray film. After development, the positions of the probe become visible.

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