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.
Which one of the following techniques is used to separate DNA fragments?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Gel electrophoresis
Option (1) PCR — Incorrect. PCR (polymerase chain reaction) makes many copies of a chosen piece of DNA in a test tube. It increases the amount of DNA; it does not sort the fragments.
Option (2) Autoradiography — Incorrect. Autoradiography detects a radioactive label by the dark spots it makes on an X-ray film. It is used to see DNA that has bound a labelled probe, as in DNA fingerprinting. The DNA must already be separated before this step.
Option (3) Electron microscopy — Incorrect. An electron microscope uses a beam of electrons to show very small structures in great detail. It gives a picture; it does not separate DNA fragments.
Option (4) Gel electrophoresis — Correct. Restriction enzymes cut DNA into fragments of different sizes. In gel electrophoresis the fragments move through an agarose gel in an electric field, and they separate by size. The smaller the fragment, the farther it moves.
Note 1: 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.
Note 2: A similar question was also asked in CUET (UG) 2026 on 29-05-2026 (Slot 1) and on 25-05-2026 (Slot 1), and in CUET (UG) 2025 on 23-05-2025 (Slot 2).
NCERT Extract:
Restriction Enzymes – …
