1) The separation on an electrophoretic gel of sequences or fragments of genomic or complementary DNA, partially digested by endonucleases, The fragments are then 'blotted' onto a membrane and allowed to hybridize with a specific, labeled probe in order to detect which bands contain the fragment or gene of interest. Southern blot is particularly useful in detecting large gene rearrangements/deletions and large trinucleotide repeat expansions.

2) Southern blotting is a laboratory technique used to detect a specific DNA sequence in a blood or tissue sample. A restriction enzyme is used to cut a sample of DNA into fragments that are separated using gel electrophoresis. The DNA fragments are transferred out of the gel to the surface of a membrane. The membrane is exposed to a DNA probe labeled with a radioactive or chemical tag. If the probe binds to the membrane, then the probe sequence is present in the sample.