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Question #45863
The Question
In a modified Griffith’s experiment, a researcher engineers the non-virulent R-strain of Streptococcus pneumoniae to express an active CRISPR-Cas9 system. The guide RNA (gRNA) in this system is designed to be perfectly complementary to the gene responsible for synthesizing the smooth polysaccharide capsule in the virulent S-strain. This engineered R-strain is mixed with heat-killed S-strain bacteria and injected into a cohort of mice. Which of the following represents the most likely outcome and its correct molecular rationale?
Options
- A.
A. The mice will die of pneumonia; CRISPR-Cas9 facilitates the targeted integration of the virulence gene into the R-strain genome.
- B.
B. The mice will survive; Cas9 endonuclease cleaves the incoming transforming principle, effectively preventing horizontal gene transfer.
- C.
C. The mice will die of pneumonia; the transforming principle is a protein, which remains unaffected by the CRISPR-Cas9 nuclease activity.
- D.
D. The mice will survive; the CRISPR-Cas9 complex directly degrades the residual polysaccharide capsule of the heat-killed S-strain.
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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
Griffith’s Transforming Principle|Restriction Enzyme Cleavage Physics|Genetic Code Degeneracy
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often associate CRISPR-Cas9 exclusively with modern biotechnological 'gene editing' (where it is hijacked to insert genes in eukaryotes) and forget its fundamental biological role as a bacterial immune system that destroys invading foreign DNA.
The trap in Option A exploits this misconception.
Option C tests the foundational NCERT knowledge of the biochemical nature of the transforming principle, while Option D tests the specific substrate specificity of the Cas9 enzyme.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Molecular Basis of Inheritance - Class 12 |
| Concept | Griffith’s Transforming Principle |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |