DNA strands on a gel stained with ethidium bromide when viewed under UV radiation, appear as

Correct answer: 3)

Concept:

• Gel electrophoresis is a method of separation of a mixture of DNA samples based on their molecular size and charge.
• Generally, agarose gel is used to carry out gel electrophoresis.

Explanation:

• Gel electrophoresis is carried out in a series of steps- agarose gel is prepared, a sample of DNA is prepared, then the mixture of DNA sample is loaded into the wells in the gel, and then an electric field is applied.
• On applying electric field DNA fragments start to move towards the positive terminal as they are negatively charged.
• This separates the sample based on size and charge.
• Ethidium bromide (EtBr) is a fluorescent dye and an intercalation agent used in gel electrophoresis.
• EtBr inserts itself in between the stacked bases. When visualized under the UV lamp, it will appear as bright orange bands.

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So, the correct answer is option 3.