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Assertion and Reason Analysis

• Assertion A: The strand separation of DNA occurs in vivo during processes such as DNA replication and transcription.
  ✅ True.
  During DNA replication and transcription, enzymes like helicases and RNA polymerase unwind and separate the double helix to expose single strands of DNA that serve as templates.

• Reason R: The sites where these processes are initiated are often rich in C/G base pairs.
  ❌ Incorrect.
  Initiation sites, such as origins of replication and promoters, are often rich in A/T base pairs, not C/G.
  This is because A-T base pairs are held together by only two hydrogen bonds, compared to the three hydrogen bonds in C-G base pairs, making them easier to separate.

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Correct Interpretation:

• A is correct: DNA strand separation is essential and does occur during replication and transcription.

• R is incorrect: Initiation sites are not rich in C/G, but rather A/T-rich for ease of strand separation.

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Correct Answer:

3. A is correct but R is not correct

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Conclusion:

While DNA strand separation is a critical step during both replication and transcription, the initiation regions are specifically designed to favor separation—hence the preference for A/T-rich sequences. The reason statement provided contradicts this fact and is therefore incorrect.