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What was the initial frequency of allele B2 before selection occurred?
What was the initial frequency of allele B2 before selection occurred?
What is the expected proportion of allele B1 after selection has occurred?
What is the expected proportion of allele B1 after selection has occurred?
Which diploid genotype had the lowest survival rate?
Which diploid genotype had the lowest survival rate?
What is the key reason for the decrease in the B2 allele frequency?
What is the key reason for the decrease in the B2 allele frequency?
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What must be considered to determine if the change in allele frequencies is significant?
What must be considered to determine if the change in allele frequencies is significant?
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What was the primary focus of the study by Cavener & Clegg on Drosophila melanogaster?
What was the primary focus of the study by Cavener & Clegg on Drosophila melanogaster?
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Which of the following describes the two alleles at the ADH locus in fruitflies?
Which of the following describes the two alleles at the ADH locus in fruitflies?
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How did Cavener & Clegg select breeders for their experimental populations?
How did Cavener & Clegg select breeders for their experimental populations?
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What was the main environmental factor manipulated in Cavener & Clegg's experiment?
What was the main environmental factor manipulated in Cavener & Clegg's experiment?
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What did the Y-axis represent in the results of Cavener & Clegg's study?
What did the Y-axis represent in the results of Cavener & Clegg's study?
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What is expected to happen to average heterozygosity as bw75 drifts toward fixation or loss?
What is expected to happen to average heterozygosity as bw75 drifts toward fixation or loss?
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What does the U-shaped distribution of allele frequencies indicate?
What does the U-shaped distribution of allele frequencies indicate?
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What effective population size was recorded in Buri's experiment?
What effective population size was recorded in Buri's experiment?
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Which event was primarily responsible for isolating the collared lizard populations in the Ozarks?
Which event was primarily responsible for isolating the collared lizard populations in the Ozarks?
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What phenomenon is indicated by the ratio of 30 lost to 28 fixed populations in Buri's experiment?
What phenomenon is indicated by the ratio of 30 lost to 28 fixed populations in Buri's experiment?
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Why might the effective population size appear smaller than the actual size in Buri's experiment?
Why might the effective population size appear smaller than the actual size in Buri's experiment?
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What aspect of the collared lizard's habitat change contributed to genetic isolation?
What aspect of the collared lizard's habitat change contributed to genetic isolation?
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After how many generations was bw75's frequency fixed in one population for the first time?
After how many generations was bw75's frequency fixed in one population for the first time?
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What is the primary difference between mutation and substitution?
What is the primary difference between mutation and substitution?
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In the context of evolutionary substitution, what occurs when a new allele is fixed?
In the context of evolutionary substitution, what occurs when a new allele is fixed?
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How does genetic drift influence the rate of substitutions in populations of varying sizes?
How does genetic drift influence the rate of substitutions in populations of varying sizes?
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What is the primary limitation of the simplest Mendelian model involving a single locus with two alleles?
What is the primary limitation of the simplest Mendelian model involving a single locus with two alleles?
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What happens to deleterious alleles in the evolution process?
What happens to deleterious alleles in the evolution process?
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When crossing two genotypes of AABB and aabb in a Mendelian model with two loci, what is the genotype of all F1 offspring?
When crossing two genotypes of AABB and aabb in a Mendelian model with two loci, what is the genotype of all F1 offspring?
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What do neutralists predict about the rate of evolution for most genes in most populations?
What do neutralists predict about the rate of evolution for most genes in most populations?
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What is indicated by the loss of the original allele in generation 19?
What is indicated by the loss of the original allele in generation 19?
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How many phenotypes are predicted in Mendel's model with six loci and 24 alleles?
How many phenotypes are predicted in Mendel's model with six loci and 24 alleles?
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What observation did Edward West's dataset reveal about plant size variation?
What observation did Edward West's dataset reveal about plant size variation?
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What does a model with six loci and increasing alleles allow for in terms of phenotypes?
What does a model with six loci and increasing alleles allow for in terms of phenotypes?
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What are two potential outcomes for neutral mutations in a population?
What are two potential outcomes for neutral mutations in a population?
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In a two loci model with four alleles, which of the following ratios is obtained in F2 offspring?
In a two loci model with four alleles, which of the following ratios is obtained in F2 offspring?
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Which statement accurately describes the process of fixation in relation to mutations?
Which statement accurately describes the process of fixation in relation to mutations?
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Why are traits influenced by many loci and many alleles more relevant to fitness?
Why are traits influenced by many loci and many alleles more relevant to fitness?
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What is one potential reason for phenotypic variation among genetically identical plants in West's experiment?
What is one potential reason for phenotypic variation among genetically identical plants in West's experiment?
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Study Notes
Selection and Allele Frequencies
- Selection can alter allele frequencies.
- A locus affecting survival probability is considered.
- A single locus with two alleles, B1 and B2, is considered for a simple selection example.
- There are three possible diploids: B1B1, B1B2, and B2B2.
- The initial frequencies of B1 and B2 are 0.6 and 0.4, respectively.
- Selection can lead to an increase in the frequency of B1 and a decrease in the frequency of B2 over time.
- Selection can favor an allele, leading to its increased prevalence in a population.
Cavener & Clegg (1981) - Drosophila melanogaster
- An experiment lasting 50 generations observed changes in allele frequencies.
- Drosophila melanogaster (fruit flies) were used as a model system.
- The experiment involved two experimental populations on food spiked with ethanol and two control populations on normal food.
- The focus was on the alcohol dehydrogenase (ADH) enzyme, which breaks down alcohol and is encoded by two alleles: AdhF (fast) and AdhS (slow).
- The results showed that the frequency of the AdhF allele increased in the populations exposed to ethanol, while the frequency of the AdhS allele decreased.
Genetic Drift Examples
- Buri's experiment with fruit flies observed random fixation and loss of heterozygosity.
- Templeton's study of collared lizards in Missouri's Ozark Mountains demonstrated the impact of habitat isolation on genetic drift.
Mendel's Model and Phenotype Variability
- Mendel's simplest model, with one locus and two alleles, fails to explain the continuous variation observed in traits like corolla length.
- Increasing the number of loci and alleles in Mendel's model leads to a wider range of phenotypes, better capturing the observed variation.
Edward West's Dataset
- West's dataset revealed continuous variation in plant size, demonstrating that individuals with the same genotype can exhibit phenotypic differences.
- This variation is attributed to environmental influences, highlighting the role of the environment in shaping phenotypic expression.
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Description
This quiz explores the impact of selection on allele frequencies using the Drosophila melanogaster model. It discusses a specific experiment by Cavener & Clegg (1981), examining allele changes over generations, especially in relation to the alcohol dehydrogenase enzyme. Test your understanding of these genetic concepts and their applications in evolutionary biology.
