NEET 2026 Botany DNA Separation and Visualization Multiple Correct Question

In this question regarding DNA separation, isolation, and visualization, we need to evaluate each statement to determine their correctness.

Correct Answer: B

Explanation of Correct Statement (B): B) The DNA fragments separate according to their size in an agarose gel, upon electrophoresis.

This statement is correct. Agarose gel electrophoresis is a widely used technique for separating DNA fragments based on their size. When an electric current is applied to the gel, negatively charged DNA molecules migrate towards the positive electrode. Smaller DNA fragments move faster and travel further through the porous agarose gel than larger fragments. The separation occurs because the gel acts like a sieve, allowing smaller molecules to pass through more easily than larger ones.

Clarification of Other Options:

A) The cutting of DNA is done by molecular scissors.

This statement is partially correct but misleading. While it's true that enzymes known as restriction endonucleases (often referred to as "molecular scissors") are used to cut DNA at specific sequences, the statement lacks context regarding the purpose of cutting. The cutting is a preliminary step for cloning, analysis, or manipulation of DNA, but the term "molecular scissors" may imply a more simplistic view of the process.

C) The separated DNA fragments can be seen without staining when exposed to UV light.

This statement is incorrect. DNA is not inherently visible under UV light without a staining agent. Typically, DNA needs to be stained with a dye, such as ethidium bromide or SYBR Green, to be visualized effectively. These dyes intercalate between the bases of the DNA and fluoresce when exposed to UV light, allowing the DNA bands to be seen.

D) The separated DNA fragments, when stained with ethidium bromide, can be seen in visible light.

This statement is incorrect. Ethidium bromide is a fluorescent dye that requires UV light for visualization. When DNA that has been stained with ethidium bromide is exposed to UV light, it fluoresces and can be visualized, but it does not emit visible light under normal circumstances. Instead, the fluorescence occurs under UV illumination, which is a different spectrum than visible light.

Summary:

• Correct Statement: B - DNA fragments do indeed separate by size in agarose gel during electrophoresis.
• Incorrect Statements: A is misleading, C is false as DNA needs staining for visibility, and D is false as ethidium bromide requires UV light for visualizing the stained DNA.

Understanding these concepts is crucial in biotechnology, particularly in techniques involving DNA manipulation and analysis.