Question

Since DNA fragments are negatively charged molecules, they can be separated by forcing them to move towards the Anode under electric field through a medium in Gel Electrophoresis. The separated DNA fragments can be visualized only after staining in Ethidium bromide followed by exposure to UV radiation. Which of the following is most appropriate?

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

EtBr intercalates into DNA double helix and fluoresces orange under UV --- used to visualise DNA bands after electrophoresis.

Answer 1

The Correct Option is B

Step 1: Concept
Gel electrophoresis and ethidium bromide staining.

Step 2: Meaning
In gel electrophoresis, negatively charged DNA migrates toward the anode; EtBr intercalates into DNA and fluoresces under UV.

Step 3: Analysis
Statement (A) is correct: DNA is negatively charged and migrates toward the anode, being separated by size through the gel matrix.
Statement (R) is also correct: EtBr staining followed by UV exposure is a standard visualisation method.
However, (R) describes visualisation --- a step after separation --- not the reason why DNA migrates toward the anode. Hence (R) is not the explanation of (A).

Step 4: Conclusion
Both (A) and (R) are correct but (R) does not explain (A). Final Answer: (B)