Questions and Answers
What are the assumptions of Hardy-Weinberg Equilibrium?
Large populations, no genetic drift, no natural selection/mutation or migration, no assortative mating/sexual selection or inbreeding.
Why do we use the Hardy-Weinberg Equilibrium if the assumptions are rarely met?
By assuming that nothing changes, we can say that any deviation from the standard signifies evolutionary change.
What additional lines of evidence are used to provide us with clues about which particular forces of evolution are responsible for the observed deviation from Hardy-Weinberg Equilibrium?
We can look at the structure/size of the population, whether it is large or small.
Why is fitness considered the 'currency' of natural selection?
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How do we calculate the absolute fitness (W) of a phenotype?
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Why is relative fitness (w) used to predict changes in allele frequencies as a result of selection instead of absolute fitness (W)?
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Why do we consider relative fitness when attempting to understand how natural selection is acting on a locus rather than using absolute fitness (W)?
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What sort of selection most likely maintains the 50:50 sex ratio seen in most populations?
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What happens to CF allele frequency when many women with CF now survive to reproduce?
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What happens to CF allele frequency due to typhoid fever being low since the twentieth century in developed nations?
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What happens to CF allele frequency when in some populations potential parents are screened for common CF alleles?
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What happens to CF allele frequency due to the emergence of drug-resistant typhoid fever in developing nations?
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Study Notes
Hardy-Weinberg Equilibrium
- Assumes large populations with no genetic drift, natural selection, mutations, migrations, assortative mating, or inbreeding.
- Serves as a null hypothesis for testing evolutionary changes.
Importance of Hardy-Weinberg Equilibrium
- Acts as a baseline; deviations indicate potential evolutionary changes.
- Useful for detecting factors influencing evolution even when assumptions are rarely met.
Evolutionary Forces
- Observing deviations from Hardy-Weinberg allows identification of evolutionary forces affecting a locus.
- Population size impacts genetic drift; larger populations are less affected by drift, while smaller populations may experience natural selection more.
- Inbreeding is less likely in larger populations and increases in isolated or separated groups.
Fitness in Natural Selection
- Fitness measures an individual’s genetic contribution to future generations, influencing selection processes.
- Higher fitness enhances the likelihood of traits being selected for in subsequent generations.
Calculating Fitness
- Absolute fitness (W) of a phenotype calculated as the product of fecundity and viability.
- Relative fitness (w) compares absolute fitness among genotypes to assess changes in allele frequencies due to selection.
Relative vs Absolute Fitness
- Relative fitness accounts for the reproductive dynamics within a population, offering a better perspective on evolutionary forces.
- Observations of allele frequencies can fluctuate due to genetic drift; larger populations minimize this randomness.
Sex Ratio and Selection
- A population with an imbalanced sex ratio experiences selective advantages for the rarer gender, impacting reproductive success and offspring production.
- Frequency-dependent selection maintains the typical 50:50 sex ratio found in many species.
Cystic Fibrosis (CF) Allele Frequency Changes
- Increased reproductive success among women with CF leads to a rise in CF allele frequency despite the sterility of affected males.
- Typhoid fever's decline in developed nations results in decreased CF allele frequency, highlighting reduced heterozygote superiority.
- Screening for CF alleles by potential parents decreases allele frequency, indicating voluntary reproductive choices.
- Drug-resistant typhoid fever surges in developing nations correlate with an increase in CF allele frequency, showcasing heterozygote superiority.
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Description
Explore the critical concepts of Hardy-Weinberg Equilibrium in this quiz. Understand the assumptions necessary for the model and the implications of deviations from it. Perfect for reinforcing your knowledge in evolutionary biology.
