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Ch. 24 - The Origin of Species
Chapter 24, Problem 5

Which of the following factors would be the most likely to contribute to allopatric speciation?


A. The separated population is large, and genetic drift occurs.
B. Selection pressures in the isolated population are similar to those in the ancestral population.
C. Gene flow between the two populations is extensive.
D. Different mutations begin to distinguish the gene pools of the separated populations.

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1
Understand the concept of allopatric speciation: Allopatric speciation occurs when a population is geographically separated into two or more isolated groups, preventing gene flow between them.
Analyze the impact of a large separated population and genetic drift: Genetic drift can lead to significant changes in small populations, but its effect is reduced in larger populations.
Evaluate the role of similar selection pressures: If selection pressures are similar in both the isolated and ancestral populations, the genetic makeup of the populations is likely to remain similar, reducing the likelihood of speciation.
Consider the effect of extensive gene flow: Extensive gene flow between two populations allows for the exchange of genetic material, which can prevent the populations from diverging significantly and thus inhibit speciation.
Assess the impact of different mutations: Different mutations in the gene pools of separated populations can lead to genetic divergence if these mutations lead to different traits that are subject to selection.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Allopatric Speciation

Allopatric speciation occurs when a population is geographically separated, leading to reproductive isolation. This separation can result from physical barriers like mountains or rivers, preventing gene flow between the groups. Over time, the isolated populations may evolve independently, potentially leading to the emergence of new species.
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Allopatric Speciation

Genetic Drift

Genetic drift is a mechanism of evolution that involves random changes in allele frequencies within a population. It is particularly significant in small populations, where chance events can lead to the loss or fixation of alleles. This can contribute to divergence between separated populations, enhancing the likelihood of speciation.
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Mutation and Gene Pool Divergence

Mutations are changes in the DNA sequence that can introduce new genetic variations into a population. When populations are isolated, different mutations can accumulate in each group, leading to distinct gene pools. This genetic divergence is crucial for speciation, as it can result in populations that are no longer capable of interbreeding.
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Related Practice
Textbook Question

Males of different species of the fruit fly Drosophila that live in the same parts of the Hawaiian Islands have different elaborate courtship rituals. These rituals involve fighting other males and making stylized movements that attract females. What type of reproductive isolation does this represent? a. habitat isolation b. temporal isolation c. behavioral isolation d. gametic isolation

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Textbook Question

According to the punctuated equilibria model, a. given enough time, most existing species will branch gradually into new species. b. most new species accumulate their unique features relatively rapidly as they come into existence, then change little for the rest of their duration as a species. c. most evolution occurs in sympatric populations. d. speciation is usually due to a single mutation.

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Textbook Question

Bird guides once listed the myrtle warbler and Audubon's warbler as distinct species. Recently, these birds have been classified as eastern and western forms of a single species, the yellow-rumped warbler. Which of the following pieces of evidence, if true, would be cause for this reclassification? a. The two forms interbreed often in nature, and their offspring survive and reproduce well. b. The two forms live in similar habitats and have similar food requirements. c. The two forms have many genes in common. d. The two forms are very similar in appearance.

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Textbook Question

Plant species A has a diploid chromosome number of 12. Plant species B has a diploid number of 16. A new species, C, arises as an allopolyploid from A and B. The diploid number for species C would probably be a. 14. b. 16. c. 28. d. 56.

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