Section 3: Genetics, Cellular and Molecular Biology
CRISPR-Cas9 gene editing
Subtopic: Fundamentals of CRISPR-Cas9 gene editing
Question Statement:
A cultured skin fibroblast cell of a goat 'P' was fused with an enucleated ovum of
a goat 'Q'. The resultant activated early embryo was then transplanted into a
pseudopregnant (surrogate) female goat 'R' of the same strain as 'Q'. On
completion of gestation, a female goat 'S' was born. With the exception of
mitochondrial DNA, 'S' is a clone of ________.
Options:
(A) Only P
(B) Only Q
(C) Only R
(D) Both P and R
Official Answer Key:
A
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2024 Q.20)**
**1. Governing Concept**:
- **Topic**: Molecular Genetics & Somatic Cell Nuclear Transfer (Cloning)
- In somatic cell nuclear transfer (SCNT):
- Donor nuclear DNA originates from the somatic cell donor (goat 'P').
- Enucleated ovum donor ('Q') provides the oocyte cytoplasm and mitochondrial DNA.
- Surrogate mother ('R') carries the pregnancy to term and provides uterine environment, but no genetic material to the offspring.
- Therefore, the nuclear genomic DNA of the cloned offspring is identical **only to P**.
**2. Option Analysis**:
- **Option (A) [Only P] is CORRECT**: The nuclear genome originates exclusively from the nucleus of fibroblast donor P.
- **Option (B) [Only Q] is INCORRECT**: Q contributes mitochondrial DNA, not nuclear genome.
- **Option (C) [Only R] is INCORRECT**: Surrogate mother R contributes zero genomic material.
- **Option (D) [Both P and R] is INCORRECT**: R has no genetic contribution.
**3. Final Answer**:
- **Correct Choice**: **A**
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