Q.9 Given below are two statements, one is labelled as Assertion (A) and other one
labelled as Reason (R).
Assertion (A) : Male sterility in angiosperms can be induced by inserting a
bacterial gene called BARNASE
Reason (R) : BARNASE causes premature breakdown of tapetum resulting in
arrest of microspore development
In light of the above statements, choose the correct answer from the options given
below.
1. Both (A) and (R) are true and (R) is the correct explanation of (A).
2. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
3. (A) is true but (R) is false.
4. (A) is false but (R) is true.
BARNASE Gene Male Sterility: Correct Answer Explained
The BARNASE gene from bacteria induces male sterility in angiosperms by targeting anther tissues. This SEO article analyzes the assertion-reason question, confirming option 1 as correct with detailed breakdowns.
Question Overview
Assertion (A): Male sterility in angiosperms can be induced by inserting a bacterial gene called BARNASE.
Reason (R): BARNASE causes premature breakdown of tapetum resulting in arrest of microspore development.
Correct Answer
Option 1: Both (A) and (R) are true and (R) is the correct explanation of (A).
BARNASE encodes a ribonuclease enzyme expressed under tapetum-specific promoters (e.g., TA29), degrading RNA in tapetal cells. This premature tapetum breakdown disrupts microspore nourishment and development, causing pollen abortion and male sterility in crops like tobacco and rapeseed.
Option Explanations
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Option 1: Correct—R directly explains A’s mechanism; tapetum destruction halts pollen formation via RNA hydrolysis.
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Option 2: Incorrect—R causally links to A; it’s not just a co-occurring fact but the precise mode of action.
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Option 3: Incorrect—R accurately describes the cytotoxic effect on tapetum, validated in multiple angiosperm studies.
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Option 4: Incorrect—A is a proven biotech method for hybrid seed production using barnase-barstar systems.
BARNASE-Barstar System Basics
| Component | Function | Role in Hybrid Breeding |
|---|---|---|
| BARNASE | RNase destroys tapetal RNA | Induces A-line sterility |
| BARSTAR | Inhibits barnase | Restores fertility in F1 hybrids |
| TA29 Promoter | Tapetum-specific expression | Targets male tissues precisely |
This genetic tool enables maintainer (B) and restorer (R) lines for commercial hybrids without chemical emasculation.
Exam Tips
Common in NEET/UGC biotech sections; remember barnase specificity to tapetum differentiates it from cytoplasmic male sterility. Pairs with barstar for reversibility.
