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Question #46772
The Question
During a gene therapy trial for Severe Combined Immunodeficiency (SCID) caused by Adenosine Deaminase (ADA) deficiency, a patient's lymphocytes are transduced with a retroviral vector carrying functional ADA cDNA. Post-transfusion, PCR analysis confirms the successful integration of the transgene into the host genome. However, the lymphocytes exhibit absolutely zero ADA enzyme activity. Which of the following is the most plausible molecular explanation for this failure?
Options
- A.
The transgene integrated into a transcriptionally inactive heterochromatic region rich in repetitive DNA sequences.
- B.
The retroviral vector failed to provide an independent origin of replication (ori) for the ADA cDNA.
- C.
The ADA cDNA integrated into a euchromatic region, leading to rapid degradation via RNA interference.
- D.
The introduced ADA cDNA lacked introns, preventing the transport of its mRNA out of the nucleus.
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
Chromatin Condensation States|Human Genome Repetitive DNA|ADA Deficiency Genetic Correction
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Distinguishing between gene 'integration' and gene 'expression'.
Students often assume that successful insertion of a gene automatically leads to its expression.
This question forces the synthesis of Biotechnology (ADA gene therapy) with Molecular Basis of Inheritance (Euchromatin vs.
Heterochromatin), highlighting that the genomic neighborhood (repetitive DNA/heterochromatin) dictates transcriptional accessibility.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Cell – The Unit of Life - Class 11 |
| Concept | Chromatin Condensation States |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |