Problem 5 - Campbell Biology

Question

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.

Step-by-Step Solution

Answer

Option (D) Different mutations begin to distinguish the gene pools of the separated populations.

Step 1 - Understand Allopatric Speciation

Allopatric speciation occurs when a population is divided by a geographical barrier, leading to the formation of two separate populations that evolve independently. Over time, genetic differences accumulate, potentially resulting in the emergence of new species.

Step 2 - Analyze Option A

option (A) suggests that genetic drift occurs in a large separated population. However, genetic drift has a more significant impact in smaller populations.

Step 3 - Analyze Option B

option (B) states that selection pressures are similar in both populations, which would not significantly contribute to divergence since both populations would evolve in similar ways.

Step 4 - Analyze Option C

option (C) mentions extensive gene flow between the populations, which would prevent them from becoming genetically distinct and reduce the likelihood of speciation.

Step 5 - Analyze Option D

option (D) proposes that different mutations accumulate in the separated populations, distinguishing their gene pools. This is the most likely factor to contribute to allopatric speciation since unique mutations would lead to genetic divergence.

Step 6 - Choose the Correct Option

Based on the analysis, option (D) is the most likely factor to contribute to allopatric speciation.

Key Concepts

Genetic Drift

Genetic drift is a mechanism of evolution. It refers to changes in the frequency of genes in a population due to random events. Unlike natural selection, which involves specific traits becoming more common for survival reasons, genetic drift is random and can affect populations of any size. However, it has a more pronounced effect on small populations. Some characteristics of genetic drift include:

• Random changes in gene frequencies
• Greater impact in small populations
• Can lead to loss of genetic variation

In the context of allopatric speciation, genetic drift could contribute to genetic differences over time, but its influence is usually limited in larger populations.

Geographical Barrier

A geographical barrier is any physical obstacle that divides a population into two or more groups, preventing them from interbreeding. This separation is crucial for allopatric speciation because it allows each group to evolve independently. Examples of geographical barriers include:

• Mountain ranges
• Rivers
• Oceans
• Deserts

Over time, the isolated groups experience different environmental pressures and genetic changes, which can lead to significant genetic divergence and, eventually, the formation of new species. The geographical barrier stops gene flow between the populations, which is essential for speciation.

Mutations

Mutations are changes in the DNA sequence of an organism. They are a primary source of genetic variation in populations and can introduce new traits. Mutations occur randomly and can be beneficial, neutral, or harmful. Some key points about mutations:

• Source of genetic diversity
• Can be spontaneous or induced by environmental factors
• May lead to new traits that can be subject to natural selection

In allopatric speciation, different mutations accumulating in the separated populations are a significant factor. These genetic differences build up over time, further distinguishing the gene pools of each group and potentially leading to the emergence of new species.

Gene Flow

Gene flow is the transfer of genetic material between populations. It occurs when individuals from different populations interbreed. Gene flow tends to reduce genetic differences between populations, making them more similar. Important aspects of gene flow include:

• Increases genetic variation within a population
• Reduces differences between populations
• Can introduce new traits

For allopatric speciation to occur, gene flow must be reduced or halted. The geographical barrier typically ensures that there is no or minimal gene flow between the isolated populations, allowing them to evolve independently.

Natural Selection

Natural selection is the process where organisms with traits better suited to their environment have higher survival and reproduction rates. This process leads to the increase in frequency of advantageous traits in the population. Key points about natural selection include:

• Acts on existing genetic variation
• Increases traits that improve survival and reproduction
• Can lead to adaptation to different environments

In the context of allopatric speciation, natural selection plays a crucial role. As populations are isolated by a geographical barrier, they encounter different environmental challenges. This leads to selection pressures that drive each population to adapt uniquely, further promoting genetic divergence and the potential formation of new species.