Which of the following statements are correct with respect to DNA separation, isolation and visualization? A. The cutting of DNA is done by molecular scissors. B. The DNA fragments separate according to their size in an agarose gel, upon electrophoresis. C. The separated DNA fragments can be seen without staining when exposed to UV light. D. The separated DNA fragments, when stained with ethidium bromide, can be seen in visible light. Choose the correct answer from the options given below:

Solution & Explanation

Answer: (Option 1) B and D only Solution: B is correct — DNA fragments separate by size in an agarose gel on electrophoresis. D is correct — fragments stained with ethidium bromide can be seen (as orange bands) under UV/visible light. A is wrong as stated because the cutting/molecular-scissors step concerns restriction digestion, not the separation-isolation-visualization process being asked. C is wrong — separated DNA cannot be seen WITHOUT staining; visualization requires ethidium bromide staining followed by UV exposure. Hence only B and D are correct. NCERT Reference: Ch 9, p.168, line(s) 17-22 — "The separated DNA fragments can be visualised only after staining the DNA with a compound known as ethidium bromide followed by exposure to UV radiation (you cannot see pure DNA fragments in the visible light and"