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Difficulty: MediumAdaptive Radiation and Mechanisms of Speciation

Arrange the following stages of allopatric speciation in the correct sequential order from first to last:

  1. 1A physical geographic barrier emerges, separating an ancestral population into geographically isolated subpopulations.
  2. 2Isolated subpopulations experience independent genetic drift, mutations, and distinct environmental selective pressures.
  3. 3Accumulated genetic differences lead to the development of pre-zygotic or post-zygotic reproductive isolation mechanisms.
  4. 4Secondary contact occurs, but the populations are unable to interbreed and produce fertile offspring.

Answer

The correct sequence of allopatric speciation begins with geographic barrier formation, followed by independent genetic divergence in isolation, leading to the development of reproductive isolation mechanisms, and culminating in complete biological speciation upon secondary contact.
Allopatric speciation requires physical geographic isolation to stop gene flow between populations. Over time, independent selective pressures and genetic drift alter gene pools until biological reproductive isolation arises, making interbreeding impossible even if secondary contact occurs.

Step-by-Step Solution

1
Identify the initial event that begins allopatric speciation.
Physical geographic separation occurs first, which cuts off gene flow between subpopulations.
Allopatric speciation is specifically defined by geographical isolation as its triggering mechanism.
2
Determine the genetic consequences while populations are geographically isolated.
Subpopulations independently undergo natural selection, mutations, and genetic drift.
Absence of gene flow permits independent changes in allele frequencies across separate environments.
3
Identify how genetic divergence leads to biological speciation.
Reproductive isolating mechanisms (e.g. mating behavior changes, gamete incompatibility) develop.
Genetic changes eventually affect traits critical for successful mating and fertilization.
4
Determine the outcome if the geographic barrier is removed.
Secondary contact reveals that the two populations can no longer interbreed to produce viable, fertile offspring.
Biological reproductive isolation confirms that distinct species have formed.

Key Concept

Stages of allopatric speciation and reproductive isolation mechanisms
Estimated Time:1m 30s
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Topics

Adaptive Radiation and Mechanisms of Speciation

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