Electrophoresis

                                      Southern Blotting

In molecular biology there are three techniques used for detecting DNA / RNA /protein ,  Southern blotting for DNA detection , Northern blotting for RNA detection and Western blotting for  detecting protein .  The term blotting is generally refers to the transferring of the   DNA /RNA / Protein into carrier like nylon membrane .  After blotting the transferred molecules are visualized by autoradiography , chromogenic detection method , silver staining method etc . This technique was developed by  Edwin Southern in 1975 .

Procedure -

• The DNA is isolated from the cell of interest .
• Now the DNA is digested by restriction enzyme . Restriction enzyme cut the DNA molecules into desired fragments .
• The fragments are separated by agrose  gel electrophoresis into different size .
• The double stranded DNA  is denature into single strands by sodium hydroxide .
• The DNA fragments are transferred onto  membrane by capillary action . There are two type of  membrane are used in this method - nitrocellulose membrane and nylon membrane .
• The small segments known as probes is labelled with either with radioactive chemical or fluorescent dye  for identification . 
• 
  The probe will bind strongly to the sequence and lead to the formation of double stranded DNA .
• The unbound molecules are removed by washing process .

Applications Of Southern Blotting -

• Southern Blotting is used for detecting particular gene in the genome .
• It is used for gene cloning .
• It determine the map position of DNA sequence in the chromosome .