Q.50 Which of the following statements made with regards to plasmid incompatibility are true ?
(A). Plasmids having the same origin of replication, belong to the same incompatibility group.
(B). Plasmids having different origins of replication, belong to the same incompatibility group.
(C). Plasmids of the same incompatibility group are compatible.
(D). Plasmids of the same incompatibility group are incompatible.
Choose the correct answer from the options given below:
1. (A) and (C) only.
2. (A) and (D) only.
3. (B) and (C) only.
4. (B) and (D) only.
Plasmid Incompatibility: Correct Statements Revealed
Plasmids with the same replication origin belong to the same incompatibility group and cannot stably coexist, making option 2: (A) and (D) only correct.
Plasmid Basics
Plasmids are extrachromosomal DNA molecules in bacteria, maintained through controlled replication via specific origins (ori).
Incompatibility arises when two plasmids compete for the same replication/partitioning machinery, leading to loss of one during cell division.
Groups are classified by shared control mechanisms, critical for cloning and genetic engineering.
Correct Statements
Option 2 identifies accurate facts: (A) and (D).
| Statement | Truth | Explanation |
|---|---|---|
| (A) Plasmids having the same origin of replication belong to the same incompatibility group | True | Shared ori/replicon causes indistinguishable replication control (antisense RNA/iterons), preventing coexistence |
| (D) Plasmids of the same incompatibility group are incompatible | True | They compete for replication factors, resulting in unstable maintenance in the same cell |
Incorrect Statements
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(B) False—different origins typically place plasmids in separate groups, allowing coexistence.
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(C) False—same group plasmids are structurally/physiologically incompatible.
Option Breakdown
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Option 1 (A, C): Wrong—(C) contradicts definition; same group = incompatible.
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Option 2 (A, D): Correct—core principles of plasmid biology.
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Option 3 (B, C): Wrong—both reversed; different ori often compatible.
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Option 4 (B, D): Wrong—(B) false despite (D) true.
Understanding incompatibility ensures successful co-transformation in molecular biology labs and exams like NEET.
