Problem 5 - Campbell Biology

Question

Application/analysis Which of the following factors would not contribute to allopatric speciation? (A) The separated population is small, and genetic drift occurs. (B) The isolated population is exposed to different selection pressures than the ancestral population. (C) Different mutations begin to distinguish the gene pools of the separated populations. (D) Gene flow between the two populations is extensive.

Step-by-Step Solution

Answer

Option D would not contribute to allopatric speciation.

Step 1: Understanding Allopatric Speciation

Allopatric speciation occurs when a population is divided by a geographical barrier, leading to genetic divergence due to the lack of gene flow between the separated groups.

Step 2: Analyzing Option A

Option A suggests that the separated population is small and genetic drift occurs. Genetic drift can lead to differences in allele frequencies, contributing to allopatric speciation.

Step 3: Analyzing Option B

Option B indicates the isolated population experiences different selection pressures. Different environmental conditions can drive natural selection in different directions, leading to speciation.

Step 4: Analyzing Option C

Option C states that different mutations distinguish the gene pools. Mutations introduce genetic variability which, under isolation, can contribute to divergence between populations.

Step 5: Analyzing Option D

Option D claims that gene flow between the two populations is extensive. Extensive gene flow maintains genetic similarity between populations, hindering the process of allopatric speciation.

Step 6: Conclusion

From the analysis, factors A, B, and C contribute to allopatric speciation, while D does not because it prevents genetic divergence by maintaining gene flow.

Key Concepts

Genetic Drift

Genetic drift is a mechanism by which allele frequencies in a population change over time due to random sampling effects. This process is particularly influential in small populations where random events can have a disproportionately large impact. For example, if a few individuals in a small population carry a unique allele, and those individuals do not reproduce, that allele can be lost entirely from the gene pool. Over time, genetic drift can lead to significant genetic divergence between populations.
In the context of allopatric speciation, genetic drift can accelerate the differences between a geographically separated population and its parent population. Since the populations are isolated, the random changes in allele frequencies due to genetic drift can contribute to genetic differences, ultimately facilitating speciation. Therefore, genetic drift plays a crucial role in the divergence of populations in allopatric speciation.

Selection Pressures

Selection pressures refer to environmental factors that influence the survival and reproductive success of organisms. These pressures can include resource availability, predation, climate, and competition for mates, among others. When populations are geographically separated, the different environmental conditions they experience impose varying selection pressures.
In allopatric speciation, differing selection pressures ensure that the separated populations adapt to their unique environments. For example, a population isolated on an island may experience different food sources and predators than the mainland population. Over time, these differences drive natural selection in distinct directions, leading to adaptations that further differentiate the populations.
Thus, differing selection pressures are a key factor in the divergence of populations and the formation of new species through allopatric speciation.

Mutations

Mutations are changes in the DNA sequence of an organism. They can occur spontaneously due to errors in DNA replication or be induced by environmental factors such as radiation or chemicals. Mutations introduce new genetic variations into a population and are a fundamental source of genetic diversity.
In the context of allopatric speciation, mutations can accumulate independently in separated populations. Without gene flow, these new mutations can become fixed in the population if they offer some advantage or simply by chance through genetic drift. Over generations, these genetic differences can contribute to the divergence of the two populations.
Mutations, therefore, play a vital role in creating the genetic diversity necessary for the differentiation and eventual formation of new species in allopatric speciation.

Gene Flow

Gene flow refers to the transfer of genetic material between populations through interbreeding. It tends to homogenize the gene pools of populations, reducing genetic differences. Effective gene flow maintains genetic similarity and prevents speciation.
In the case of allopatric speciation, geographical barriers prevent or severely limit gene flow between populations. This isolation is crucial because the lack of gene flow allows for genetic drift, differing selection pressures, and independent mutations to drive the genetic divergence of the populations.
As indicated in the exercise analysis, extensive gene flow between separated populations would counteract the effects of genetic drift, differing selection pressures, and mutations, thereby hindering allopatric speciation. Thus, limited or absent gene flow is essential for the populations to diverge sufficiently to become separate species.