Q.100 Which one of the following factors does NOT contribute to “allopatric speciation”?
(A) The isolated population is exposed to different selection pressure as compared to parent
population
(B) A population become geographically isolated from the parent population
(C) There is a gene flow between the two separated populations
(D) Genetic drift occurs between the two separated populations
Answer: (C) There is a gene flow between the two separated populations
Allopatric speciation requires complete geographic isolation to prevent gene exchange, allowing populations to diverge genetically over time. Option C directly opposes this by implying ongoing gene flow, which maintains genetic similarity and blocks speciation.
Option Analysis
Option (A): The isolated population faces different selection pressures, driving adaptive divergence like beak shape changes in Darwin’s finches across Galápagos islands. This contributes strongly to allopatric speciation.
Option (B): Geographic isolation via barriers like rivers or mountains forms the foundation, halting interbreeding as seen in Grand Canyon squirrel populations.
Option (C): Gene flow between populations mixes alleles, counteracting divergence and preventing reproductive isolation essential for speciation.
Option (D): Genetic drift accelerates fixation of random alleles in small isolates, enhancing differences from the parent group.
Allopatric speciation occurs when populations diverge due to geographic isolation, a key process in evolutionary biology for CSIR NET exams. Geographic barriers prevent gene flow, enabling factors like selection and drift to foster new species.
Key Contributing Factors
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Geographic isolation splits populations, as in vicariance events like rising mountains.
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Different selection pressures adapt isolates to local environments, promoting reproductive barriers.
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Genetic drift randomizes alleles in small groups, accelerating divergence.
Non-Contributing Factor
Gene flow between separated populations homogenizes genetics, negating allopatric speciation by sustaining similarity despite isolation. This contrasts with sympatric speciation lacking barriers.
