How do the separation occur: DNA fragments are separated according to their size and charge.
Gel-Electrophoresis (DNA): A solution of DNA molecules is placed in to a gel. The gel is coated with a dye to allow the researchers or anyone else to see the DNA form within the gel. The image shows that the DNA is placed into a gel at the negative and runs in the direction of the positive end. This happens because DNA is negatively charged and causes it to migrate towards the positive electrode when placed in an electrical field. As the DNA travels from negative to positive a series of 'bands' begin to form containing DNA molecules of certain size. The bands that are located at the positive end of the gel contain small fragments of DNA. The bands that are closest to the start of the gel contain the largest DNA fragments.
