Assertion: DNA ligase plays an important role in recombinant DNA technology.
Reason: The linking of antibiotic resistance gene with plasmid vector became possible by enzyme DNA ligase

Options

A. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).
B. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion then mark (2).
C. If Assertion is true but Reason are false, then mark(3).
D. If both Assertion and Reason are false, then mark(4).

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "DNA ligase plays an important role in recombinant DNA technology."
- DNA ligase is indeed crucial in this field as it facilitates the joining of DNA fragments.

2. **Defining DNA Ligase**:
- DNA ligase is an enzyme that is often referred to as "molecular glue."
- Its primary function is to form phosphodiester bonds between adjacent nucleotides, which allows it to covalently link individual fragments of DNA.

3. **Function of DNA Ligase**:
- The enzyme uses energy from the cell to perform its function of joining DNA fragments.
- This process is essential for creating stable recombinant DNA molecules.

4. **Understanding the Reason**:
- The reason provided states that "the linking of antibiotic resistance gene with plasmid vector became possible by enzyme DNA ligase."
- This is accurate because, during recombinant DNA technology, DNA ligase is used to join the antibiotic resistance gene with the plasmid vector after the vector has been cut by restriction enzymes.

5. **Process of Linking**:
- The plasmid vector is cut at a specific site by restriction endonucleases.
- The antibiotic resistance gene is then inserted into this cut site.
- DNA ligase is employed to seal the nicks in the sugar-phosphate backbone, thus linking the gene to the vector.

6. **Conclusion**:
- Both the assertion and the reason are true.
- The reason correctly explains why the assertion is true, as DNA ligase is essential for linking DNA fragments in recombinant DNA technology.

### Final Answer:
Both the assertion and the reason are true, and the reason provides the correct explanation for the assertion.

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