Q.32 Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R.
Assertion A: Monkeys and chimpanzees cannot mate in present day conditions.
Reason R: Reproductive isolation is reversible.
In the light of the above statements, choose the most appropriate answer from the options given below:
- Both A and R are correct and R is the correct explanation of A
- Both A and R are correct but R is NOT the correct explanation of A
- A is correct but R is not correct
- A is not correct but R is correct
Monkeys and chimpanzees cannot mate due to reproductive isolation in modern biology exams.
Monkeys and chimpanzees belong to different genera and cannot produce viable offspring today because of established reproductive barriers. This assertion-reason question tests understanding of speciation and isolation mechanisms.
Question Breakdown
Assertion A states that monkeys and chimpanzees cannot mate under present-day conditions, reflecting prezygotic and postzygotic barriers like genetic divergence and hybrid inviability. Reason R claims reproductive isolation is reversible, which contradicts core evolutionary biology where isolation is typically a one-way process leading to permanent species divergence.
Option Analysis
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Both A and R correct, R explains A: Incorrect. While A holds true due to millions of years of separation (monkeys: ~40 million years ago; apes: more recent), R fails as reversibility would imply merging species, not explaining the barrier.
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Both A and R correct, but R does not explain A: Wrong. R is false; isolation solidifies via mutations and natural selection, not reversal.
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A correct, R incorrect: Correct. A aligns with biological species concept—monkeys (Cercopithecidae) and chimpanzees (Hominidae) show ~93% DNA similarity but no fertile hybrids; R misstates isolation as irreversible in nature.
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A incorrect, R correct: False. A is accurate, and R does not hold as seen in lab hybrids (e.g., no monkey-chimp success).
Correct Answer
A is correct but R is not correct. This matches CUET PG 2023 analysis.
Introduction to Reproductive Isolation
In evolutionary biology, monkeys and chimpanzees cannot mate in present day conditions because they represent distinct primate lineages separated by reproductive isolation. This barrier ensures no viable offspring, a key speciation factor. For students tackling assertion-reason questions, understanding this clarifies why such isolation is not reversible.
Why Assertion A Holds True
Monkeys (e.g., macaques) diverged from ape lines ~25-40 million years ago, accumulating chromosomal differences (humans/chimps: 46 vs. typical monkey counts). Chimpanzees mate within species via promiscuity but reject cross-genus pairing due to behavioral, gametic, and developmental blocks. No documented fertile hybrids exist today.
Debunking Reason R
Reproductive isolation is reversible? No—it’s a cumulative process via genetic drift, selection, and mutations. Rare lab reversals (e.g., polyploid plants) don’t apply to animals like primates, where isolation becomes permanent. R misleads by suggesting easy reversal, unfit as A’s explanation.
Exam Strategy for Assertion-Reason
Target competitive exams like GATE Life Sciences or CUET PG:
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Verify A independently (fact-check via species concept).
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Test R’s truth and linkage to A.
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Practice: Similar questions on horse-donkey sterility emphasize postzygotic isolation.
Option Validity Why? 1: Both correct, R explains False R untrue 2: Both correct, no explanation False R untrue 3: A true, R false True Matches biology 4: A false, R true False A factual This format aids quick revision for your molecular biology focus.
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