Question

A mixture containing DNA fragments a, b, c and d, with molecular weights of $a + b = c$, $a > b$, and $d > c$ was subjected to agarose gel electrophoresis. The positions of these fragments from cathode to anode sides of the gel would be
a. B, A, C, D
b. A, B, C, D
c. C, B, A, D
d. B, A, D, C

Answer 1

Hint: Agarose gel electrophoresis is a technique in which the DNA strands are cut according to the need and then are made to separate based on their size on the agarose gel using electrophoresis. Or we can say that the electric current is passed on the gel and the fragments align themselves according to their sizes.

Complete answer:
Agarose gel electrophoresis is mainly used in biochemistry and genetics where the separation of DNA, RNA, or protein fragments is required. The DNA is cut into small fragments and is then planted in the wells made in the agarose gel base. This base is prepared by the solution containing agarose which acts as a semi solidifying agent. The electric current is passed on from the negative end of the anode to the cathode. So, the negatively charged DNA fragments travel to the cathode end of the tray.
The fragments which are smaller in size travel very fast and are present in the cathode region and the heavy or bulky fragments are present in the anode region of the agarose base. The DNA fragments can be visualized easily due to the presence of the intercalating agent known as ethidium bromide. The DNA fragments light up under the UV light and are present in the form of bands. As the ‘d’ fragment is greater than the ‘c’ and ‘c’ is formed from the addition of ‘a’ and ‘b’. So we can say that ‘d’ is the largest fragment followed by c, b, and ‘a’ being the smaller fragments in the row.

So, the answer is ‘B, A, C, D’.

Note:
This technique is only used for separating the desired gene that one has to study. This is a basic technique that is used in northern blotting, Southern blotting, and western blotting.