Electrophoresis and role of ethidium bromide:

Electrophoresis is a technique used to separate and sometimes purify macromolecules. While charged molecules are placed in an electric field, they migrate towards either the positive or negative pole. Proteins and nucleic acids differ in size, charge or conformations. Therefore, they are analyzed through following the movement of proteins and nucleic acids driven through a potential gradient in a thick media.  This method is widely-used techniques within biochemistry and molecular biology.

Ethidium bromide is a fluorescent dye having subsequent structure:

This compound intercalates among bases of nucleic acids. Outside DNA, it does not have fluorescence whereas intercalated ethidium bromide shows fluorescence at the visible region.  This phenomenon permits a convenient detection of DNA fragments in gels.