DNA electrophoresis under UV light. Close-up of a DNA (deoxyribonucleic acid) electrophoresis gel viewed under UV (ultraviolet) light. Gel electrophoresis is a technique used to analyse the molecular composition of DNA samples. The extracted DNA is placed into a gel, which then has an electrical current passed through it that separates the DNA molecules based on their size and charge. The technique is also used to analyse the protein composition of cells and tissues.