DNA are-vely charged, forced to move towards anode, electric field agarose gel matrix, separate according to their size / sieving effect, smaller fragments moves faster and further than the larger.
Since DNA fragments are negatively charged molecules. They can be separated by forcing them to move towards the anode under an electric field through a medium/matrix. The most commonly used matrix is agarose which is a natural polymer extracted from sea weeds.
The DNA fragments separate according to their size through sieving effect provided by the agarose gel.Hence, the smaller the fragment size,the farther it moves.