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 ________.
Only P
Only Q
Only R
Both P and R
ANSWER
S is a clone of Only P (Option A).
Official answer: ASource: Official answer key, GATE 2024 BT (IISc Bengaluru)
Identify the technique: fusing a somatic (skin fibroblast) nucleus from goat P with an enucleated ovum (cytoplasm only) from goat Q is somatic cell nuclear transfer (SCNT) — the method used to create Dolly.
In SCNT, the embryo's nuclear genome is entirely that of the nucleus donor (P), because the ovum's own nucleus was removed before fusion.
The ovum donor (Q) contributes only cytoplasm, and therefore only mitochondria/mitochondrial DNA. The question explicitly excludes mtDNA from the comparison, so Q's sole genetic contribution is removed from consideration.
The surrogate mother (R) supplies only the uterine environment for gestation. Despite being of the same strain as Q, R contributes no nuclear or mitochondrial DNA to S — gestating in a surrogate does not change the fetus's genotype.
Since S's nuclear DNA is 100% identical to P's, and mtDNA (from Q) is explicitly excluded, S is genetically a clone of only P.
Evaluate options: (A) Only P — correct; (B) Only Q — incorrect, Q's only contribution (mtDNA) is excluded; (C) Only R — incorrect, R contributed no genetic material; (D) Both P and R — incorrect, R contributed nothing genetic.
KEY IDEA
In somatic cell nuclear transfer (SCNT), the clone's nuclear genome comes entirely from the somatic-nucleus donor; the enucleated-ovum donor contributes only mitochondria (excluded here by the question), and the surrogate mother contributes no genetic material at all, only the uterine environment for gestation.
WATCH OUT FOR
Assuming the surrogate mother R, "of the same strain as Q," must therefore also be genetically related to Q (or to S) and choosing (D) Both P and R — surrogacy provides gestation only, not genetic contribution.
From the GATE 2024 BT paper. Every question of this paper · Download the full paper · All 10 Mendelian genetics questions, with notes
