Read the following passage carefully and answer the given questions.
The separated DNA fragments can be visualized only after staining the DNA with ethidium bromide followed by exposure to UV radiation. Bright orange colored bands of DNA in ethidium bromide stained gel exposed to UV light can be seen. The separated bands of DNA are cut out from the agarose gel and extracted from the gel piece. This step is known as elution. The DNA fragments purified in this way are used in constructing recombinant DNA by joining them with a cloning vector.
The DNA fragments are separated by-
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Forcing them to move towards anode under an electric field
Option (1) Forcing them to move towards anode under an electric field — Correct. DNA has phosphate groups in its backbone, so DNA fragments carry a negative charge. In an electric field they are pulled towards the positive electrode, the anode.
Option (2) Forcing them to move towards cathode under an electric field — Incorrect. The cathode is the negative electrode. A negative charge is pushed away from it, so DNA never moves towards the cathode.
Option (3) Forcing them to move towards anode under an electromagnetic field — Incorrect. The direction is right, but the field is wrong. Gel electrophoresis uses an electric field set up by a current between two electrodes, not an electromagnetic field.
Option (4) Forcing them to move towards cathode under an magnetic field — Incorrect. Both parts are wrong. A magnetic field does not drive charged DNA through a gel, and negatively charged DNA moves away from the cathode.
Note: This passage is taken from NCERT as it is. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
NCERT Extract:
Restriction Enzymes – …
