Southern blot
The Southern blot is a technique to detect the presence of a specific piece of DNA sequence. It is named after Edward M. Southern who developed the technique at Edinburgh University in the 1970 [1].
The Process
The DNA in which has to be tested for the specific sequence gets cut into pieces by an enzyme.
Afterwards gel electrophoresis is used to separate those pieces by size on an agarose gel.
Alkali is used to denaturate the DNA fragments and the they are transfered to a nitrocellulose filter or nylon membrane by blotting.
The filter gets incubated with a single stranded DNA probe. That probe is either radiocativly marked or marked with an enzyme.
If the probe is marked radiocativly it can be exposed with X-ray's. Otherwise a substance is added that gets a color through interaction with the enzyme. [2][3].