Assertion: Foreign DNA and vector DNA are cut with the help of ligase.
Reason: Ligase does not act on sugar-phosphate backbone of DNA.

Options

A. Both A and R are true and R is the correct explanation of A
B. Both A and R are true and R is not the correct explanation of A.
C. A is true but R is false.
D. A is false but R is true.

Explanation

To analyze the assertion and reason provided in the question, we will break down the statements and evaluate their correctness step by step.

### Step 1: Understand the Assertion
The assertion states that "Foreign DNA and vector DNA are cut with the help of ligase."
- **Evaluation**: This statement is incorrect. Ligase is an enzyme that is used to join or seal DNA fragments together, not to cut them. The cutting of DNA is typically performed by restriction endonucleases, which are enzymes that recognize specific sequences in DNA and cleave the sugar-phosphate backbone.

### Step 2: Understand the Reason
The reason states that "Ligase does not act on the sugar-phosphate backbone of DNA."
- **Evaluation**: This statement is also incorrect. Ligase does act on the sugar-phosphate backbone, but its function is to seal the nicks or gaps in the backbone after DNA has been cut. It does not cut the DNA; instead, it facilitates the joining of DNA fragments by forming phosphodiester bonds between the sugar and phosphate groups.

### Step 3: Conclusion
Based on the evaluations:
- The assertion is false because ligase does not cut DNA.
- The reason is misleading because while ligase does interact with the sugar-phosphate backbone, it does not cut it; instead, it seals it.

### Final Answer
- The assertion (A) is false.
- The reason (R) is also misleading and can be considered false in the context of the assertion.