Section 3: Genetics, Cellular and Molecular Biology
CRISPR-Cas9 gene editing
Subtopic: Fundamentals of CRISPR-Cas9 gene editing
Question Statement:
CRISPR-Cas system is associated with
Options:
(A) adaptive immunity in eukaryotes
(B) adaptive immunity in prokaryotes
(C) innate immunity in eukaryotes
(D) innate immunity in prokaryotes
Official Answer Key:
B
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2021 Q.21)**
**1. Governing Concept**:
- **Topic**: Molecular Biology & Prokaryotic Immune Systems
- The **CRISPR-Cas** (Clustered Regularly Interspaced Short Palindromic Repeats) system is an RNA-mediated **adaptive immune system in prokaryotes** (bacteria and archaea) that protects against invading bacteriophages and conjugative plasmids through sequence-specific cleavage of foreign nucleic acids.
**2. Option Analysis**:
- **Option (A) is INCORRECT**: CRISPR is not an endogenous eukaryotic immune system.
- **Option (B) [adaptive immunity in prokaryotes] is CORRECT**: Canonical biological function of CRISPR-Cas in bacteria/archaea.
- **Option (C) is INCORRECT**: Eukaryotic innate immunity employs pattern recognition receptors (TLRs).
- **Option (D) is INCORRECT**: Bacterial restriction-modification is innate; CRISPR provides memory/adaptation.
**3. Final Answer**:
- **Correct Choice**: **B**
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