Answer to Question #343709 in Genetics for acey

Question

The following fragments were obtained after digestion of a sequence using restriction enzymes: 5.3 kb, 2.1 kb, 6.8 kb, 3.6 kb, 1.1 kb, 2.2 kb. Order the fragments, moving from the fastest migration to the slowest migration on a gel. Which two fragments may be difficult to isolate on a gel? Why? Sketch the resulting gel after running the fragments on it. Assume that the fragments were all run in one lane. Label the positions of the positive and negative electrodes. 

Answer 1

The fragments with the smallest molecular mass will move the fastest in the gel, since they will more easily bypass obstacles in the form of pores of different diameters in the gel.

Accordingly, if you order the fragments by gradual decreasing the rate of their migration in the gel, then the order will be as follows:

1.1 kb, 2.1 kb, 2.2 kb, 3.6 kb, 5.3 kb, 6.8 kb.

Fragments with molecular masses of 5.3 kb and 6.8 kb are the most difficult to isolate on the gel for the reason that, due to their mass, they are also large in size, and because of this, they practically cannot budge, since this will be hindered by the friction force on the pores of the gel.

If you use the order of fragments that is specified in the condition, then the gel will look like this:

Since the charge of the fragments is negative, then, accordingly, they will move towards the positive electrode.