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Question #45809
The Question
Sickle cell anemia is a classic example of pleiotropy, where a single genetic locus affects multiple phenotypic traits, including erythrocyte morphology, oxygen affinity, and malaria resistance. Which of the following statements regarding the molecular and physiological basis of this condition is INCORRECT?
Options
- A.
The primary phenotypic effect of the mutant allele is the polymerization of hemoglobin molecules under low oxygen tension, which subsequently alters the biconcave shape of the RBC.
- B.
The substitution of glutamic acid by valine at the sixth position of the beta-globin chain represents the replacement of a hydrophilic amino acid with a hydrophobic one.
- C.
The HbS allele exhibits pleiotropy because the mutated gene undergoes alternative splicing to directly produce multiple distinct abnormal proteins that independently target the spleen and erythrocyte cytoskeleton.
- D.
At the organismal level, the disease phenotype is recessive, but at the molecular level, the HbA and HbS alleles exhibit co-dominance in heterozygous individuals.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Regulatory_Failure
Understand how NOT, EXCEPT, and logical constraints are used to manipulate exam results.
Concepts Behind This Question
Sickle_Cell_Anemia|Hemoglobin|Autosomal_Recessive
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often misunderstand the mechanism of pleiotropy.
They mistakenly believe a pleiotropic gene must directly produce multiple different proteins (e.g., via alternative splicing) or directly participate in multiple independent pathways.
The trap tests the understanding of 'cascade pleiotropy', where a single primary protein defect (mutant beta-globin) causes a domino effect of physiological consequences (sickling -> vaso-occlusion -> splenic sequestration -> malaria resistance).
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Principles of Inheritance and Variation - Class 12 |
| Concept | Pleiotropy Logic |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |