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Ch. 20 - Population Genetics and Evolution at the Population, Species, and Molecular Levels
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
All textbooksSanders 3rd EditionCh. 20 - Population Genetics and Evolution at the Population, Species, and Molecular LevelsProblem 8
Chapter 20, Problem 8

Catastrophic events such as loss of habitat, famine, or overhunting can push species to the brink of extinction and result in a genetic bottleneck. What happens to allele frequencies in a species that experiences a near-extinction event, and what is expected to happen to allele frequencies if the species recovers from near extinction?

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1
Understand the concept of a genetic bottleneck: A genetic bottleneck occurs when a population's size is significantly reduced for at least one generation, leading to a loss of genetic diversity.
Consider the initial impact on allele frequencies: During a bottleneck, allele frequencies can change dramatically due to genetic drift, which is the change in the frequency of an allele due to random sampling of organisms.
Recognize the potential for reduced genetic variation: With fewer individuals, there is less genetic variation, which can lead to certain alleles becoming fixed (reaching a frequency of 1) or lost (reaching a frequency of 0).
Analyze the recovery phase: If the species recovers, the population size increases, but the genetic diversity may remain low because the gene pool is limited to the alleles present in the surviving individuals.
Consider long-term effects: Over time, mutations and gene flow from other populations can introduce new alleles, potentially increasing genetic diversity, but the initial loss of diversity can have lasting effects on the population's adaptability.

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Key Concepts

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

Genetic Bottleneck

A genetic bottleneck occurs when a population's size is significantly reduced for at least one generation, leading to a loss of genetic diversity. This reduction can result from catastrophic events like habitat loss or overhunting, which limit the number of individuals that contribute to the gene pool. Consequently, the allele frequencies in the surviving population may shift, often leading to increased prevalence of certain alleles while others may be lost entirely.
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Allele Frequencies

Allele frequencies refer to how often a particular allele appears in a population's gene pool. In the context of a genetic bottleneck, the frequencies can change dramatically due to the reduced genetic diversity. If a species recovers from near extinction, the allele frequencies may stabilize over time, but they may not return to their original state, potentially leading to a population that is less adaptable to environmental changes.
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Population Recovery and Genetic Diversity

When a species recovers from a near-extinction event, the genetic diversity may remain low if the recovery is based on a small number of individuals. This limited genetic diversity can hinder the population's ability to adapt to new environmental challenges. Over time, if the population grows and individuals interbreed, allele frequencies may shift again, potentially restoring some genetic diversity, but the initial loss from the bottleneck can have long-lasting effects on the population's evolutionary trajectory.
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Related Practice
Textbook Question

Consider possible societal and ethical dilemmas that might arise if we currently shared the planet with another hominin.

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Textbook Question
Over the course of many generations in a small population, what effect does random genetic drift have on allele frequencies?
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Textbook Question

Carl Linnaeus, the 18th-century botanist who laid the foundation for the modern system of taxonomic nomenclature, placed chimpanzees and humans in the same genus. Discuss the merits of this classification.

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Describe how selection at a locus can result in a loss of polymorphism surrounding the locus.

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George Udny Yule was wrong in suggesting that an autosomal dominant trait like brachydactyly will increase in frequency in populations. Explain why Yule was incorrect.
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Textbook Question

How can ancient DNA provide insight into past migrations that analyses of extant human genomes fail to uncover?