Read the passage and answer the following question :
The cutting of DNA by restriction endonucleases results in the fragments of DNA. These fragments can be separated by a technique known as gel electrophoresis. Since DNA fragments are negatively charged molecules, they can be separated by forcing them to move towards the anode under an electric field through a medium/matrix. The commonly used matrix is agarose which is a natural polymer extracted from sea weeds. The DNA fragments separate according to their size through sieving effect provided by the agarose gel. Hence, the smaller fragments move farther in the agarose gel. The separated DNA fragments can be visualised only after staining the DNA with ethidium bromide followed by exposure to UV radiation. Bright orange coloured bands of DNA can be observed. 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 cloning vectors.
The separated DNA fragments can be visualised after staining with___________, followed by exposure to__________.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Ethidium bromide, UV radiation
Option (1) β-galactosidase, UV radiation — Incorrect. β-galactosidase is an enzyme used in blue-white selection of recombinants, not a stain for DNA. The UV (ultraviolet) radiation part is right.
Option (2) β-galactosidase, Gamma radiation — Incorrect. Both parts are wrong: an enzyme is not a stain, and gamma rays are not used to view DNA.
Option (3) Ethidium bromide, UV radiation — Correct. DNA stained with ethidium bromide and exposed to UV (ultraviolet) light shows as bright orange bands.
Option (4) Ethidium bromide, Gamma radiation — Incorrect. The stain is right, but the bands are seen under UV, not gamma radiation.
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.