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Question #45599
The Question
Sickle cell anaemia provides a classic insight into allelic interactions and evolutionary biology. Which of the following statements regarding this condition is INCORRECT?
Options
- A.
The defect arises from a point mutation resulting in the substitution of Glutamic acid by Valine at the sixth position of the beta-globin chain.
- B.
In carriers (HbA HbS), the alleles exhibit co-dominance at the molecular level, as both normal and mutant beta-globin chains are synthesized.
- C.
The condition exemplifies pleiotropy, where a single gene mutation alters haemoglobin structure, erythrocyte morphology, and susceptibility to malaria.
- D.
The HbS allele behaves as a completely recessive allele for both the expression of sickle cell disease and the trait of resistance against Plasmodium falciparum.
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
HbA|HbS|Pleiotropy|Beta-Globin_Chain
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often rigidly classify alleles as strictly 'dominant' or 'recessive' based solely on the primary disease phenotype.
This trap exploits the failure to recognize that dominance is not an autonomous feature of an allele, but depends entirely on the specific phenotype being observed (e.g., clinical anaemia vs. malarial resistance).
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Principles of Inheritance and Variation - Class 12 |
| Concept | Co-dominance Allelic Interaction |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |