a) How do DNA fragments migrate and resolve in Gel electrophoresis?

b) How is lane one different from lane 2, 3 and 4 in the Gel electrophoresis set up?

c) How are pure DNA fragments made observable in the visible light?

(a) Separation of DNA fragments is done by gel electrophoresis. The DNA fragments are negatively charged and hence are separated by forcing them to move towards a positive end (anode) under an electric field through a medium. This medium or matrix is a natural polymer extracted from sea weeds: agarose.

The agarose gel provides a sieving effect by which DNA fragments are separated according to their size. The smaller fragments of DNA thus move to a farther distance.

(b) Lane 1 shows the migration of undigested DNA fragments. They are a mixture of DNA fragments produced by the random cutting of the DNA and hence appear as different sized fragments.

Lane 2, 3, 4 shows the digested set of DNA fragments, where the restriction endonucleases cut the DNA at specific sites along the DNA chain and fragments thus obtained are same sized.

(c) Staining the DNA with ethidium bromide and then exposing them to UV radiation can make pure DNA fragments observable in visible light.