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Compare and contrast stabilizing, directional and disruptive selection with regard to how each affects the mean phenotype of the population as well as the variance in the phenotype.

Compare and contrast stabilizing, directional and disruptive selection with regard to how each affects the mean phenotype of the population as well as the variance in the phenotype.

Human Anatomy & Physiology (11th Edition)
Human Anatomy & Physiology (11th Edition)
11th Edition
ISBN:9780134580999
Author:Elaine N. Marieb, Katja N. Hoehn
Publisher:Elaine N. Marieb, Katja N. Hoehn
Chapter1: The Human Body: An Orientation
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**Title: Understanding Selection in Population Genetics** **Text:** When studying population genetics, it’s crucial to understand how various types of selection affect the mean phenotype and the variance within a population. Here, we will compare and contrast stabilizing, directional, and disruptive selection with respect to these aspects: **1. Stabilizing Selection:** - **Mean Phenotype:** Stabilizing selection favors the intermediate phenotypes, reducing the extremes. Thus, the mean phenotype remains largely unchanged but becomes more common in the population. - **Variance in Phenotype:** This type of selection reduces the variance in the phenotype because it discourages deviations from the average. **2. Directional Selection:** - **Mean Phenotype:** Directional selection favors one extreme phenotype over the other. As a result, the mean phenotype shifts in the direction of the favored extreme. - **Variance in Phenotype:** This can reduce or maintain the variance depending on whether the selection pressure is consistent and strong. **3. Disruptive Selection:** - **Mean Phenotype:** Disruptive selection favors both extremes of the phenotypic range over the average phenotype. It does not necessarily change the mean phenotype immediately, but it increases the frequency of extreme phenotypes. - **Variance in Phenotype:** This type of selection increases variance because it encourages diverseness in the population. **Conclusion:** Understanding the differing impacts of stabilizing, directional, and disruptive selection on mean phenotype and phenotypic variance is fundamental for geneticists studying evolutionary processes. Each type of selection leaves a distinct signature on the population's genetic structure that can drive evolutionary change in various ways. **Graphs and Diagrams:** In the context of explaining these concepts, diagrams illustrating normal distributions before and after each selection type could be useful. - **Stabilizing Selection Diagram:** This would show a narrowing of the bell curve around the mean. - **Directional Selection Diagram:** This would display a shift of the bell curve toward one extreme. - **Disruptive Selection Diagram:** This would illustrate the separation of the bell curve into two peaks at the extremes. Such visual aids can help in better grasping the variations in trait distributions due to different selection pressures.
Transcribed Image Text:**Title: Understanding Selection in Population Genetics** **Text:** When studying population genetics, it’s crucial to understand how various types of selection affect the mean phenotype and the variance within a population. Here, we will compare and contrast stabilizing, directional, and disruptive selection with respect to these aspects: **1. Stabilizing Selection:** - **Mean Phenotype:** Stabilizing selection favors the intermediate phenotypes, reducing the extremes. Thus, the mean phenotype remains largely unchanged but becomes more common in the population. - **Variance in Phenotype:** This type of selection reduces the variance in the phenotype because it discourages deviations from the average. **2. Directional Selection:** - **Mean Phenotype:** Directional selection favors one extreme phenotype over the other. As a result, the mean phenotype shifts in the direction of the favored extreme. - **Variance in Phenotype:** This can reduce or maintain the variance depending on whether the selection pressure is consistent and strong. **3. Disruptive Selection:** - **Mean Phenotype:** Disruptive selection favors both extremes of the phenotypic range over the average phenotype. It does not necessarily change the mean phenotype immediately, but it increases the frequency of extreme phenotypes. - **Variance in Phenotype:** This type of selection increases variance because it encourages diverseness in the population. **Conclusion:** Understanding the differing impacts of stabilizing, directional, and disruptive selection on mean phenotype and phenotypic variance is fundamental for geneticists studying evolutionary processes. Each type of selection leaves a distinct signature on the population's genetic structure that can drive evolutionary change in various ways. **Graphs and Diagrams:** In the context of explaining these concepts, diagrams illustrating normal distributions before and after each selection type could be useful. - **Stabilizing Selection Diagram:** This would show a narrowing of the bell curve around the mean. - **Directional Selection Diagram:** This would display a shift of the bell curve toward one extreme. - **Disruptive Selection Diagram:** This would illustrate the separation of the bell curve into two peaks at the extremes. Such visual aids can help in better grasping the variations in trait distributions due to different selection pressures.
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