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Question #46496
The Question
In regions with high Plasmodium falciparum endemicity, the HbS allele is maintained at unusually high frequencies despite being lethal in the homozygous state. Which of the following statements INCORRECTLY describes the physiological and evolutionary dynamics of this phenomenon?
Options
- A.
The release of haemozoin, a toxic derivative of haemoglobin breakdown, is significantly reduced in HbA HbS individuals due to premature splenic clearance of infected RBCs.
- B.
The selective pressure of malaria drives directional selection, progressively shifting the population's allele frequency towards the fixation of the HbS allele.
- C.
Plasmodium-induced hypoxia in the erythrocytes of heterozygotes accelerates the polymerization of mutant β-globin chains, halting the parasite's replication cycle.
- D.
The persistence of the deleterious HbS allele alongside the normal HbA allele is a result of heterozygote advantage, preventing allele frequency drift towards zero.
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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
Plasmodium falciparum|HbS Allele|Selection Pressure|Heterozygote Advantage
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often confuse 'selection for a trait' with 'directional selection'.
While the HbS allele is selected for in malaria-endemic regions, it is only advantageous in the heterozygous state.
Therefore, the evolutionary mechanism is balancing selection, not directional selection.
Failing to distinguish between these modes of natural selection, while simultaneously integrating the physiological trigger (hypoxia-induced polymerization) and pathological outcome (haemozoin release), is a high-yield NEET trap.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Human Health and Disease - Class 12 |
| Concept | Haemozoin Release |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |