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Question #47726
The Question
In the treatment of Adenosine Deaminase (ADA) deficiency using traditional retroviral vectors, the viral DNA integrates into the host lymphocyte genome. Unlike the strict regulation of the origin of replication ('Ori') in prokaryotes that ensures single-event replication, retroviral integration is non-targeted. If this integration occurs adjacent to a host proto-oncogene, which of the following best describes the subsequent cellular and immunological consequences?
Options
- A.
The viral insert acts as an unregulated 'Ori', causing the ADA gene to replicate multiple times during a single S-phase, leading to ADA toxicity and cell death.
- B.
The integration overrides the host's checkpoint by activating the proto-oncogene, leading to clonal expansion and the potential presentation of neo-antigens that trigger an autoimmune-like destruction of the modified cells.
- C.
The retrovirus induces targeted homologous recombination, which permanently arrests the modified lymphocytes in the phase, preventing therapeutic ADA expression.
- D.
The integration selectively mutates the host's p53 gene, causing the lymphocytes to bypass the checkpoint without synthesizing the ADA enzyme, worsening the immunodeficiency.
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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
Agrobacterium_Tumefaciens_Mechanism|Blue-White_Screening|Transgenic_Animal_Purpose
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize that retroviruses are used for ADA gene therapy but fail to connect random integration (insertional mutagenesis) with cell cycle dysregulation (oncogene activation) and subsequent immune surveillance.
The trap in Option A plays on the concept of 'Ori' stringency, testing if students understand that eukaryotic replication control relies on licensing factors, preventing multiple replications per S-phase even if a viral sequence is introduced.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Biotechnology : Principles and Processes - Class 12 |
| Concept | Blue-White Screening Mechanism |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |