Assertion : DNA segments can be excised by 'molecular scissors or chemical scalpals' what biotechnologists call restriction enzymes.
Reason: Restriction enzymes are synthesized by microbes as a defence mechanism are specific endonucleases which can cleave double stranded DNA.

Options

A. If both Assertion and Reason are true and Reason is a correct explanation of the Assertion.
B. If both Assertion and Reason are true but Reason is not a correct explanation of the Assertion.
C. If Assertion is true but Reason is false.
D. If both Assertion and Reason are false.

Answer

**Step-by-Step Solution:**

1. **Understanding the Assertion**:
The assertion states that DNA segments can be excised by what biotechnologists refer to as restriction enzymes, which are likened to 'molecular scissors' or 'chemical scalpels'. This means that these enzymes are capable of cutting DNA at specific locations.

2. **Evaluating the Reason**:
The reason provided explains that restriction enzymes are synthesized by microbes as a defense mechanism. It also mentions that these enzymes are specific endonucleases that can cleave double-stranded DNA. This indicates that restriction enzymes play a role in the protection of microbes against foreign DNA, such as that from viruses.

3. **Analyzing the Truth of the Assertion**:
The assertion is true because restriction enzymes do indeed function to cut DNA segments at specific sequences, which is a fundamental aspect of molecular biology and biotechnology.

4. **Analyzing the Truth of the Reason**:
The reason is also true. Restriction enzymes are produced by bacteria and other microorganisms to defend against invading viruses (bacteriophages) by cutting their DNA, thus preventing infection.

5. **Determining the Relationship**:
Since both the assertion and the reason are true, and the reason provides a correct explanation for the assertion (as it describes why restriction enzymes are referred to as molecular scissors), we conclude that the relationship between the two statements is valid.

6. **Final Conclusion**:
Therefore, both the assertion and the reason are correct, and the reason is the correct explanation of the assertion.

**Answer**: Both assertion and reason are true, and the reason is the correct explanation of the assertion.

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