Q.61 Given below are two statements:
Statement-I: Allopatric speciation requires thousands to millions of years and thousands of generations.
Statement-II: Allopatric speciation occurs commonly in plants through polyploidy.
In the light of the above statements, choose the correct answer from the options given below:
(A) Both Statement-I and Statement-II are true
(B) Both Statement-I and Statement-II are false
(C) Statement-I is true but Statement-II is false
(D) Statement-I is false but Statement-II is true
Statement-I is true, but Statement-II is false, so the correct answer is (C).
Statement Analysis
Allopatric speciation occurs when populations are geographically isolated, leading to genetic divergence via mutation, selection, and drift over extended periods—typically thousands to millions of years and thousands of generations, depending on generation time and isolation strength. Statement-I is accurate. Statement-II is incorrect: polyploidy causes sympatric speciation (no geographic isolation needed), common in plants via autopolyploidy or allopolyploidy; allopatric speciation in plants is rarer and not primarily polyploid-driven.
Option Breakdown
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(A) Both true: Incorrect; II wrongly attributes polyploidy to allopatric process.
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(B) Both false: Incorrect; I reflects standard timescales (e.g., snapping shrimp: 3-15M years).
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(C) I true, II false: Correct; matches evolutionary biology consensus.
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(D) I false, II true: Incorrect; polyploidy defines sympatric speciation hallmark.
Introduction: Allopatric Speciation Time Scale and Plants Polyploidy
Allopatric speciation requires thousands to millions of years and thousands of generations for geographic isolation to yield reproductive barriers. Plants commonly undergo speciation through polyploidy, but this is sympatric, not allopatric. Master these distinctions for NEET evolution MCQs on Statement-I and II.
Allopatric Speciation Process
Geographic barriers (rivers, mountains) split populations:
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Divergence via drift, mutation, selection over 10³-10⁶ years.
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Examples: Galápagos finches, snapping shrimp (3-15M years).
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Not instant; needs sustained isolation.
Polyploidy in Plant Speciation
Polyploidy (extra chromosome sets) is sympatric:
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Autopolyploidy: Chromosome doubling in one species.
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Allopolyploidy: Hybrid + doubling (e.g., wheat, Tragopogon).
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Instant reproductive isolation; common in 15%+ angiosperms, rare in animals.
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Not allopatric: Occurs without geography.
MCQ Solution: Statement-I and Statement-II
Question: I: Allopatric speciation needs thousands-millions years/generations. II: Allopatric common in plants via polyploidy.
| Option | Evaluation |
|---|---|
| (A) Both true | Wrong; II confuses with sympatric |
| (B) Both false | Wrong; I is core definition |
| (C) I true, II false | Correct; polyploidy = sympatric |
| (D) I false, II true | Wrong; reverses mechanisms |
Answer: (C)
Exam Relevance
NEET tests allopatric (geographic) vs. sympatric (polyploidy in plants); Darwin’s finches exemplify former, wheat the latter. Key for biodiversity evolution.
