Separation and Isolation of DNA Fragments (Gel Electrophoresis) 

• Gel electrophoresis is a technique for separating DNA fragments based on their size. 

• Firstly, the sample DNA is cut into fragments by restriction endonucleases. 

• The DNA fragments being negatively charged can be separated by forcing them to move towards the anode under an electric field through a medium/matrix. 

• Commonly used matrix is agarose, which is a natural linear polymer of D-galactose and 3, 6-anhydro-L-galactose which is extracted from sea weeds. 

• The DNA fragments separate-out (resolve) according to their size because of the sieving property of agarose gel. Hence, the smaller the fragment size, the farther it will move. 

• The separated DNA fragments are visualised after staining the DNA with ethidium bromide followed by exposure to UV radiation. 

• The DNA fragments are seen as orange coloured bands. 

• The separated bands of DNA are cut out and extracted from the gel piece. This step is called elution. 

• The purified DNA fragments are used to form recombinant DNA which can be joined with cloning vectors.