This photo shows a layer of agarose gel used in the electrophoresis of the DNA. An UV light below allows us to see the DNA fragments, marked with special colors, that are traveling to the negative pole. Thank to the restriction enzymes that cut specific sites of the DNA chain, and the polymorphisms that DNA has, we obtain different leght fragments that will travel to the negative pole with different speeds, creating the blue bands that you can see in the photo.This method is used to compare samples of DNA and trace the source of a sample.