Q.105 Increasing estradiol (E2) hormone from ovarian follicles prior to ovulation has been hypothesized
to play a critical role for induction of pheromones. These pheromones render females sexually
receptive to males to facilitate mating. An investigator performs experiments in sheep in which
females are gonadectomized, then treated with E2 or vehicle alone and allowed to breed. Which
one of the findings listed below will validate the hypothesis that pheromones are induced by E2?
(A) Sexual receptivity is regained only in vehicle treated females.
(B) Sexual receptivity is regained only in E2 treated females
(C) Sexual receptivity was regained irrespective of E2 treatment
(D) Sexual receptivity is not regained by any treatment
Estradiol (E2) induces pheromones that restore sexual receptivity in gonadectomized sheep, validating the hypothesis when only E2-treated females regain mating behavior.
The correct answer is (B).
Experiment Design
Gonadectomized (ovariectomized) sheep lack ovarian hormones like E2, eliminating natural pheromones and receptivity. Vehicle (control) gets no E2; E2 group receives hormone to test pheromone induction. Breeding tests receptivity—hypothesis holds if E2 specifically restores it via pheromones attracting males.
Option Breakdown
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(A) Sexual receptivity only in vehicle-treated: Wrong—vehicle lacks E2, so no pheromone induction; both should fail without hormone.
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(B) Sexual receptivity only in E2-treated: Correct—E2 mimics preovulatory surge, induces pheromones, restores receptivity selectively, proving causation.
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(C) Receptivity irrespective of treatment: Wrong—equal response implies E2 irrelevant; hypothesis requires E2-specific effect.
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(D) No receptivity in any: Wrong—total failure doesn’t test hypothesis; E2 must work for validation.
Introduction to Estradiol E2 Pheromones Sexual Receptivity Sheep
Estradiol e2 pheromones sexual receptivity sheep studies show preovulatory E2 surge induces pheromones for mating readiness—key GATE Life Sciences concept. Gonadectomized ewes treated with E2 vs vehicle test this: only E2 restores receptivity, proving hypothesis.
Experiment Key Findings
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Ovariectomy removes E2 → no pheromones → no receptivity.
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E2 treatment: Induces pheromones, males detect, breeding succeeds.
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Vehicle: No change, confirming E2 specificity.
Option Analysis Table
| Option | Why Valid/Invalid |
|---|---|
| (A) Vehicle only | Fails—lacks E2 mechanism. |
| (B) E2 only | Matches—direct E2 → pheromones → receptivity. |
| (C) Both | Nonspecific, disproves hypothesis. |
| (D) Neither | No validation possible. |
GATE Relevance
Estradiol e2 pheromones sexual receptivity sheep PYQs test hormone-behavior links. Focus specificity in controls for scoring.
