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Question #45318
The Question
In a species of the family Solanaceae, a single pleiotropic transcription factor regulates both the anthocyanin biosynthetic pathway (floral pigmentation) and the expression of pistil-specific S-RNases involved in gametophytic self-incompatibility. If a plant undergoes a homozygous null mutation for this gene, which of the following best describes the resulting reproductive and phenotypic dynamics?
Options
- A.
The plant produces white flowers and becomes self-compatible, as the pistil fails to synthesize the enzymes required to degrade the RNA of self-pollen tubes.
- B.
The plant produces white flowers and exhibits complete male sterility, as the pollen tubes undergo premature bursting due to the absence of callose plugs.
- C.
The plant produces brightly colored flowers but fails to set seed upon self-pollination due to the hyperactivation of F-box proteins in the pollen.
- D.
The plant produces white flowers and remains strictly self-incompatible, as the lack of S-RNase triggers massive callose deposition at the stigmatic surface.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Evolutionary_Exception
Tackle problems where standard rules evolve or change based on specific environmental constraints.
Concepts Behind This Question
S-alleles|Callose deposition|Pollen rejection
Why This Question Is Tricky
Common Mistakes
The Conceptual Pivot lies in understanding that Self-Incompatibility is an 'active rejection' mechanism, not a passive requirement for fertilization.
A common misconception is that mutating an SI gene leads to sterility.
In reality, knocking out the S-RNase gene removes the barrier to self-fertilization, making the plant self-compatible.
Combining this with Pleiotropy tests the student's ability to simultaneously track a morphological outcome (loss of pigment) and a physiological outcome (loss of pollen rejection) from a single genetic locus.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Sexual Reproduction in Flowering Plants - Class 12 |
| Concept | Pollen-Pistil Interaction |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |