Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A): Plasmid can replicate independently but not a DNA fragment separated from a eukaryotic chromosome.
Reason (R): Plasmid contain replication origin.
In light of the above statements, choose the correct answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

To replicate inside a host cell, any vector or DNA molecule must have a functional Origin of Replication (ori).
Without an ori, independent replication is impossible.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Replication of any DNA molecule within a cell requires a specific sequence recognized by the host cell's replication proteins to initiate DNA synthesis.

Step 2: Detailed Explanation:
- Assertion (A) evaluation: Plasmids are extrachromosomal circular DNA molecules that replicate autonomously (independent of the host chromosome). Conversely, a random DNA fragment isolated from a eukaryotic chromosome cannot replicate independently when introduced into a host cell. Thus, Assertion (A) is true.
- Reason (R) evaluation: Plasmids possess a specific DNA sequence called the origin of replication (ori). This sequence is recognized by DNA polymerases and replication enzymes to initiate synthesis. A random genomic fragment lacks this origin and is quickly degraded or diluted out. Thus, Reason (R) is true.
- Explanation check: The presence of the ori site is the exact reason why plasmids can replicate autonomously, making (R) the correct explanation of (A).

Step 3: Final Answer:
Both (A) and (R) are true and (R) is the correct explanation of (A). This corresponds to option (A).