$ The enzymes which joins short pieces DNA in the laggins strand is called ligase.
! Lagging strand and leading strand are formed due to replication fork.

Options

A. If both As and R are correct and R is correct explanation of As
B. If both As and R are correct but R is not correct explanation of As
C. If As is correct, R is wrong
D. If both As and R are wrong.

Answer

To solve the question regarding the assertion and reason about DNA replication, we can break it down into clear steps:

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "The enzyme which joins short pieces of DNA in the lagging strand is called ligase."
- **Explanation**: This statement is true because during DNA replication, the lagging strand is synthesized in short segments known as Okazaki fragments. The enzyme DNA ligase is responsible for joining these fragments together to form a continuous strand.

2. **Understanding the Reason**:
- The reason states that "Lagging strand and leading strand are formed due to replication fork."
- **Explanation**: This statement is also true. The replication fork is the area where the DNA double helix is unwound to allow for replication. The leading strand is synthesized continuously in the direction of the fork, while the lagging strand is synthesized in short segments away from the fork.

3. **Evaluating the Relationship**:
- Now we need to determine if the reason provided is a correct explanation of the assertion.
- The reason explains the context in which the lagging strand is formed and indirectly supports the assertion about ligase's role in joining the fragments. Therefore, the reason does correctly explain the assertion.

4. **Conclusion**:
- Since both the assertion and reason are correct, and the reason is a correct explanation of the assertion, we conclude that the correct answer is: "If both assertion and reason are correct and reason is correct explanation of assertion."

### Final Answer:
The correct option is: "If both assertion and reason are correct and reason is correct explanation of assertion."

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