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Question #45354
The Question
In human fertilization, the exocytosis of cortical granules ensures the modification of the zona pellucida to prevent polyspermy. If a chemical inhibitor specifically blocks this cortical reaction in a human ovum, what will be the immediate genetic consequence upon exposure to multiple sperms, and how does this contrast with the 'physiological polyspermy' observed in Urodele amphibians?
Options
- A.
Formation of a viable polyploid embryo in humans due to multiple pronuclei fusion; whereas in Urodeles, polyspermy strictly leads to early embryonic lethality.
- B.
Integration of supernumerary sperm nuclei leading to lethal triploidy or tetraploidy in humans; whereas in Urodeles, extra sperm nuclei naturally degenerate to maintain a diploid zygote.
- C.
Failure of the secondary oocyte to complete Meiosis II, resulting in an aneuploid zygote in humans; whereas in Urodeles, multiple sperms trigger simultaneous meiotic divisions.
- D.
Immediate sustained depolarization of the oolemma causing zygotic death in humans; whereas in Urodeles, the fast block to polyspermy is permanently absent allowing normal diploidy.
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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
Cortical_Reaction|Zona_Pellucida|Species_Specific_Recognition
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often assume polyspermy universally leads to polyploidy and death across all taxa.
The trap lies in failing to distinguish between the strict mammalian reliance on the cortical reaction (where failure guarantees lethal polyploidy) and the evolutionary exception of physiological polyspermy in certain amphibians (where supernumerary sperm nuclei are actively degraded to preserve diploidy).
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Human Reproduction - Class 12 |
| Concept | Meiotic Arrest Points |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |