Questions and Answers
What might be the effect of eliminating malaria on the frequency of the S allele in a population with a high frequency of this allele?
Which type of natural selection is characterized by the selection against extreme phenotypes?
Which of the following is an example of disruptive selection?
How does natural selection for polygenic traits differ from single-gene traits?
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What could happen to the phenotype distribution under stabilizing selection?
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What characteristic of the sickle-cell allele (S) contributes to its persistence in the gene pool despite being harmful?
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How does natural selection affect allele frequencies in a population?
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Which genotype has the highest fitness in relation to malaria resistance?
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What condition is caused by the sickle-cell mutation in the hemoglobin gene?
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Why do individuals with the AA genotype have reduced fitness in malaria-prone regions?
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Natural selection leads to changes in allele frequencies within a population.
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Individuals with the SS genotype have the highest fitness due to their resistance to malaria.
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Heterozygotes with the AS genotype have a fitness advantage in malaria-prone areas.
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The allele for sickle-cell anemia is dominant over the normal allele.
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Individuals with genotype AA are completely resistant to malaria.
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Eliminating malaria in an African population with a high frequency of the S allele could potentially decrease the fitness of individuals with this allele.
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Disruptive selection results in a narrower range of phenotypes by favoring those at both extremes while selecting against those in the middle.
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Directional selection narrows the phenotypic distribution by selecting against one of the extreme phenotypes.
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Stabilizing selection can result in an increased variation of a trait within a population.
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Sickle-cell trait is influenced by multiple genes and represents a polygenic trait.
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Study Notes
Fitness and Natural Selection
- Fitness refers to an organism's ability to adapt to its environment, though various forms of fitness exist beyond just survival.
- Natural selection operates when fitness varies among individuals in a population, allowing certain traits to become more common over generations.
- Changes in allele frequencies within a population arise from differential genetic contribution by more "fit" individuals.
Sickle Cell Disease and Natural Selection
- Sickle-cell anemia is caused by a mutation in the hemoglobin gene, leading to sickle-shaped red blood cells.
- Genotypes with associated fitness levels:
- AA (normal hemoglobin): Reduced fitness due to lack of malaria resistance.
- AS (sickle-cell trait): Highest fitness, provides malaria resistance.
- SS (sickle-cell anemia): Significantly reduced fitness due to the disease.
- Heterozygotes (AS) enjoy a fitness advantage since they are less likely to succumb to malaria, which helps maintain the S allele in the population.
Impact of Environmental Changes on Fitness
- If malaria were removed from regions with high frequencies of the S allele, fitness levels among genotypes would change.
- AA genotypes may become more favorable, potentially decreasing the frequency of the S allele in those populations.
Natural Selection in Polygenic Traits
- Sickle-cell trait displays simple inheritance, while polygenic traits exhibit more complex patterns of natural selection.
- Types of natural selection affecting polygenic traits:
- Stabilizing Selection: Favors intermediate phenotypes, reduces variation (e.g., human birth weight).
- Directional Selection: Favors one extreme phenotype, shifting distributions (observed in Galápagos finches’ beak sizes).
- Disruptive Selection: Favors extreme phenotypes at both ends, often seen in sexual dimorphism (differences in male and female traits).
Examples and Context
- Human birth weight illustrates stabilizing selection, where extremes reduce survival rates.
- Directional selection observed in finches leads to adaptations based on environmental pressures.
- Disruptive selection results in distinct male and female characteristics, emphasizing the variation within species.
Fitness and Natural Selection
- Fitness refers to an organism's ability to adapt to its environment, though various forms of fitness exist beyond just survival.
- Natural selection operates when fitness varies among individuals in a population, allowing certain traits to become more common over generations.
- Changes in allele frequencies within a population arise from differential genetic contribution by more "fit" individuals.
Sickle Cell Disease and Natural Selection
- Sickle-cell anemia is caused by a mutation in the hemoglobin gene, leading to sickle-shaped red blood cells.
- Genotypes with associated fitness levels:
- AA (normal hemoglobin): Reduced fitness due to lack of malaria resistance.
- AS (sickle-cell trait): Highest fitness, provides malaria resistance.
- SS (sickle-cell anemia): Significantly reduced fitness due to the disease.
- Heterozygotes (AS) enjoy a fitness advantage since they are less likely to succumb to malaria, which helps maintain the S allele in the population.
Impact of Environmental Changes on Fitness
- If malaria were removed from regions with high frequencies of the S allele, fitness levels among genotypes would change.
- AA genotypes may become more favorable, potentially decreasing the frequency of the S allele in those populations.
Natural Selection in Polygenic Traits
- Sickle-cell trait displays simple inheritance, while polygenic traits exhibit more complex patterns of natural selection.
- Types of natural selection affecting polygenic traits:
- Stabilizing Selection: Favors intermediate phenotypes, reduces variation (e.g., human birth weight).
- Directional Selection: Favors one extreme phenotype, shifting distributions (observed in Galápagos finches’ beak sizes).
- Disruptive Selection: Favors extreme phenotypes at both ends, often seen in sexual dimorphism (differences in male and female traits).
Examples and Context
- Human birth weight illustrates stabilizing selection, where extremes reduce survival rates.
- Directional selection observed in finches leads to adaptations based on environmental pressures.
- Disruptive selection results in distinct male and female characteristics, emphasizing the variation within species.
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Description
Explore the concepts of fitness and natural selection in this quiz. Delve into how traits evolve over generations and the impact of sickle cell disease on genetic fitness. Test your understanding of these vital biological principles.
