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Question #45135
The Question
In an attempt to provide a permanent cure for Adenosine Deaminase (ADA) deficiency, functional ADA cDNA is introduced into bone marrow stem cells using a retroviral vector. However, historical clinical trials revealed that some patients subsequently developed leukemia. Which of the following best explains the molecular basis of this adverse outcome?
Options
- A.
The retroviral vector integrated randomly near a proto-oncogene, leading to insertional mutagenesis and clonal expansion.
- B.
The functional ADA cDNA underwent homologous recombination with the mutated ADA gene, triggering somatic mosaicism.
- C.
The continuous expression of the ADA enzyme in stem cells led to the toxic accumulation of deoxyadenosine triphosphate (dATP).
- D.
The viral vector reverted to its pathogenic form and selectively destroyed the T-lymphocytes, causing secondary malignancies.
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
Adenosine_Deaminase|Retroviral_Vector|Bone_marrow_cells
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize that retroviruses are standard vectors for animal cells (NCERT) but fail to connect the mechanism of retroviral integration with the inherent risks of genetic modification.
The trap lies in distinguishing between the therapeutic goal (ADA expression) and the vector's mechanical side effect (random integration causing insertional mutagenesis).
Option C is a classic 'Half-Truth' trap, reversing the actual function of the ADA enzyme.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Biotechnology and Its Applications - Class 12 |
| Concept | Insulin Chain Maturation |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |