Biotechnology: Principles and Processes
Read the following passage carefully and answer the given questions.
Biotechnology deals with large scale production and marketing of products and processes using live organisms, cells or enzymes. Modern biotechnology using genetically modified organisms was made possible only when man learnt to alter the chemistry of DNA and construct recombinant DNA. This key process is called recombinant DNA technology or genetic engineering. This process involves the use of restriction endonucleases, DNA ligase, appropriate plasmid or viral vectors to isolate and ferry the foreign DNA into host organisms, expression of the foreign gene, purification of the gene product, i.e., the functional protein and finally making a suitable formulation for marketing. Restriction endonucleases are used in genetic engineering to form ‘recombinant’ molecules of DNA, which are composed of DNA from different sources (genomes). Vectors used at present, are engineered in such a way that they help easy linking of foreign DNA and selection of recombinants from non-recombinants.
In agarose gel electrophoresis, the separated DNA fragments can be visualised with the help of -
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Ethidium bromide
In agarose gel electrophoresis, DNA fragments move towards the positive electrode, and the smaller fragments move farther. Pure DNA cannot be seen in visible light. So the gel is stained with ethidium bromide and exposed to UV radiation. The DNA then shows as bright orange bands.
(1) Bromophenol blue — Incorrect. It is not the stain that makes DNA bands visible.
(2) Acetocarmine — Incorrect. It is a stain for chromosomes in cell preparations, not for DNA in a gel.
(3) Ethidium bromide — Correct. It stains the DNA, and the stained DNA glows under UV light.
(4) Aniline Blue — Incorrect. It is a plant tissue stain, not a DNA stain for gels.
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 20-05-2026 (Slot 2), and in CUET (UG) 2025 on 20-05-2025 (Slot 2), on 16-05-2025 (Slot 1) and on 14-05-2025 (Slot 1).
NCERT Extract:
Restriction Enzymes – …
