Question

Given below are two statements:
Statement I: Plasmids are autonomously replicating DNA.
Statement II: Plasmids are extrachromosomal DNA.
In the light of the above statements, choose the most appropriate answer from the options given below:

• A. Statement I is incorrect but Statement II is correct
• B. Both Statement I and Statement II are correct
• C. Both Statement I and Statement II are incorrect
• D. Statement I is correct but Statement II is incorrect

Hint:

Plasmids are widely used as vectors in recombinant DNA technology to deliver genes of interest into host bacteria. Plasmids often carry selectable marker genes, such as those conferring resistance to antibiotics like ampicillin.

Answer 1

The Correct Option is B

Step 1: Read both statements.
Statement I: plasmids are autonomously replicating DNA. Statement II: plasmids are extrachromosomal DNA.
Step 2: Recall what plasmids are.
Plasmids are small, circular, double-stranded DNA molecules found in bacteria and some fungi, separate from the main chromosome.
Step 3: Test Statement I.
Plasmids carry their own origin of replication (ori), so they can copy themselves independently of the host chromosome. So Statement I is correct.
Step 4: Test Statement II.
Because they sit outside and apart from the chromosomal DNA, plasmids are indeed extrachromosomal. So Statement II is correct.
Step 5: Note their use.
This self-replicating, extrachromosomal nature is exactly why plasmids are used as vectors in genetic engineering.
Step 6: Conclude.
Both statements are correct, which is option (2).
\[ \boxed{\text{Both Statement I and Statement II are correct}} \]