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Hardy-Weinberg Equilibrium Activity
Introduction: In this activity, beans will be used to represent alleles in a population. Black-eyed peas will represent a dominant allele (A). Black beans will represent a recessive allele (a). The Hardy-Weinberg law of equilibrium predicts that allele frequencies will not change in a population if the population meets five conditions. State the five conditions of the Hardy-Weinberg law of equilibrium: 1. 2. 3. 4. 5. The following activity will help you test this law using five different scenarios. In Scenario #1 we will try to meet all the conditions stated above. In each Scenario #2, #3, #4 and #5 we will break one of the conditions of the Hardy-Weinberg law to see how it affects the allele frequency in a population. After each scenario you will be asked to analyze your results to see if the allelic frequency changed. Fill in the blanks below for the following information using your prior knowledge, then perform the activities in each scenario individually or with a partner. Homozygous Dominant Genotype: Heterozygous Genotype: Homozygous Recessive Genotype:
Scenario #1: A Population at Genetic Equilibrium 1. Place 50 beans of each color into a cup, these beans represent the alleles available in the gene pool of your population. Shake them well. Keep an empty cup available for step 6. 2. For each generation of offspring born out of this population, you will need to fill in the chart below. The information for Generation 1 is already filled into the chart because the scenario begins with a population of heterozygotes (Aa) who have each contributed a black-eyed peas (A) and a black bean (a) to the population in equal amounts - 50% or 0.5 of the beans represent the black-eyed peas allele and 50% or 0.5 beans represent the black bean allele at the beginning of this scenario.
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a. What do you think will happen to the frequency of the dominant blackeyed peas alleles (A) over the course of five generations? Support your answer with logic.
b. What do you think will happen to the frequency of the recessive black bean alleles (a) over the course of five generations? Support your answer with logic.
3. Remove pairs of beans from the cup to represent an individual – the two beans represent the two alleles for a single trait. “Make” 25 individuals by drawing pairs of beans from the cup until a total of 50 beans have been pulled and laid out on your desk in pairs. 4. Return unused beans (those still in the cup) to the stockpile because they did not survive. 5. Fill in the chart below with the allele frequency information for the 25 individuals laid out on your desk that you have “made”. This is generation 2 on the chart below. Calculate each allele frequency for p and q by counting the total number of each color bean out of 50 beans. 6. The total number of each color bean survived. The survivors do what they do best and that is reproduce. Return that number of each color bean to the empty cup with their offspring. (Ex. If you had 26 black-eyed peas on your desk and 24 black beans on your desk, add another 26 black-eyed peas and 24 black beans from the stockpile cup to make a total of 52 black-eyed peas and 48 black beans in the empty cup). The beans placed in the empty cup will now be the gene pool of your population for the next round. The cup should have 100 beans at the beginning of each generation. 7. Repeat steps 3-6 three more times until you have completed 5 generations, filling in the chart at the appropriate place each time.
Genotype Generation 1 Generation 2 Generation 3 Generation 4 Generation 5
AA 0
Aa 25
aa 0
p .5
p2
q2
2pq
q .5
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#2: Selection Against Homozygous Recessive Individuals
1. Repeat steps 1-7 from Scenario #1 above, but during this scenario, if two black beans are drawn to “make” an individual, return them to the gene pool and try again. 2. This scenario represents what would happen to the frequency of an allele if the homozygous recessive genotype resulted in the death of an individual prior to reproduction. In this case the homozygous recessive individuals will die – and so they do not go on to be part of the gene pool for the next generation. a. What do you think will happen to the frequency of the dominant blackeyed pea alleles (A) over the course of five generations? Support your answer with logic.
b. What do you think will happen to the frequency of the recessive black bean alleles (a) over the course of five generations? Support your answer with logic.
Complete chart below after each generation of individuals are drawn.
Genotype Generation 1 Generation 2 Generation 3 Generation 4 Generation 5
AA 0
Aa 25
aa 0
p .5
q .5
p2
q2
2pq
Scenario #3: Selection Against Homozygous Dominant Individuals 1. Repeat steps 1-7 from Scenario #1 above, but during this scenario, if two black-eyed peas are drawn to “make” an individual, return them to the gene pool and try again. 2. This scenario represents what would happen to the frequency of an allele if the homozygous dominant genotype resulted in the death of an individual prior to reproduction. In this case the homozygous dominant individuals will die – and so they do not go on to be part of the gene pool for the next generation.
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a. What do you think will happen to the frequency of the dominant blackeyed pea alleles (A) over the course of five generations? Support your answer with logic.
b. What do you think will happen to the frequency of the recessive black bean alleles (a) over the course of five generations? Support your answer with logic.
Complete chart below after each generation of individuals are drawn.
Genotype Generation 1 Generation 2 Generation 3 Generation 4 Generation 5
AA 0
Aa 25
aa 0
p .5
q .5
p2
q2
2pq
Scenario #4: Heterozygote Advantage in a Population
1. Repeat steps 1-7 from Scenario #1 above, but during this scenario, if two black beans are drawn to “make” an individual, return them to the gene pool and draw again. 2. If two black-eyed peas are drawn, flip a coin. If it is heads, return the beans to the gene pool. If tails, keep the set and record it as an individual that was added to the gene pool of the next generation. 3. This scenario represents what would happen to the frequency of an allele if the presence of the homozygous recessive genotype resulted in death of an individual and the homozygous dominant genotype resulted in a possible death. In this case the homozygous recessive individuals will die – and so they do not go on to be part of the gene pool for the next generation, while some of the homozygous dominant individuals die and others go on to become part of the gene pool for the next generation. a. What do you think will happen to the frequency of the dominant blackeyed peas alleles (A) over the course of five generations? Support your answer with logic.
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b. What do you think will happen to the frequency of the recessive black bean alleles (a) over the course of five generations? Support your answer with logic.
Complete chart below after each generation of individuals are drawn.
Genotype Generation 1 Generation 2 Generation 3 Generation 4 Generation 5
AA 0
Aa 25
aa 0
p .5
q .5
p2
q2
2pq
Scenario #5: Genetic Drift in a Population 1. Set up the cup o’beans as in step 1 (Place 50 beans of each color into a cup, these beans represent the alleles available in the gene pool of your population). Shake them well. 2. Before drawing any pairs, split the cup into three sub-populations without paying attention to the ratio of black-eyed peas to black beans in each cup – make one cup with 30 beans, another cup with 30 beans and the last cup with 40 beans. 3. For each generation of offspring born out of this population, you will need to fill in the chart below. The information for Generation 1 represents a parent population of heterozygotes (Aa) who have each contributed a black-eyed peas (A) and a black bean (a) to the population in equal amounts – 50% or 0.5 of the beans represent the black-eyed pea allele and 50% or 0.5 beans represent the black bean allele at the beginning of this scenario. However, this population has been fragmented into smaller populations prior to Generation 2. a. What do you think will happen to the frequency of the dominant black-eyed pea alleles (A) over the course of five generations in this sub-population? Support your answer with logic.
b. What do you think will happen to the frequency of the recessive black bean alleles (a) over the course of five generations in this sub-population? Support your answer with logic.
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Use 30 beans to “make” 10 individuals for five generations.
Genotype Generation 1 Generation 2 Generation 3 Generation 4 Generation 5
AA 0
Aa 10
aa 0
p .5
q .5
p2
q2
2pq
Use 30 beans to “make” 10 individuals for five generations.
Genotype Generation 1 Generation 2 Generation 3 Generation 4 Generation 5
AA 0
Aa 10
aa 0
p .5
q .5
p2
Use 40 beans to “make” 10 individuals for five generations.
Genotype Generation 1 Generation 2 Generation 3 Generation 4 Generation 5
AA 0
Aa 10
aa 0
p .5
q .5
p2
q2
2pq
Reflection Questions: Scenario #1: 1. Explain why you got the allele frequency results that were recorded.
2. What do you predict the frequency of p and q would have been if you continued the simulation for another ten generations? Explain your reasoning.
q2
2pq
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3. Explain which Hardy-Weinberg condition was broken in this scenario. You must explain your answer to receive credit.
4. Can you think of a population that would represent all the conditions of the Hardy-Weinberg law in real life? Justify your response.
Scenario #2: 5. Explain why you got the allele frequency results that were recorded.
6. What do you predict the frequency of p and q would have been if you continued the simulation for another ten generations? Explain your reasoning.
7. Explain which Hardy-Weinberg condition (in addition to the condition named in Reflection Question #3) was broken in this scenario. You must explain your answer to receive credit.
8. This scenario represents a real life situation where the homozygous recessive genotype results in an individual that does not live to reproductive age. Name one real life situation/disease where this scenario is true.
9. What would have to happen in order for a deleterious recessive allele to be completely eliminated from the gene pool?
Scenario #3: 10. Explain why you got the allele frequency results that were recorded.
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11. What do you predict the frequency of p and q would have been if you continued the simulation for another ten generations? Explain your reasoning.
12. Explain which Hardy-Weinberg condition (in addition to the condition named in Reflection Question #3) was broken in this scenario. You must explain your answer to receive credit.
13. This scenario represents a real life situation where the homozygous dominant genotype results in an individual that does not live to reproductive age. Name one real life situation/disease where this scenario is true.
14. What would have to happen in order for a deleterious dominant allele to be completely eliminated from the gene pool?
Scenario #4: 15. Explain why you got the allele frequency results that were recorded.
16. What do you predict the frequency of p and q would have been if you continued the simulation for another ten generations? Explain your reasoning.
17. ]Explain which Hardy-Weinberg condition (in addition to the condition named in Reflection Question #3) was broken in this scenario. You must explain your answer to receive credit.
18. This scenario represents a real life situation where the homozygous recessive genotype results in an individual that does not live to reproductive age and an individual with a homozygous dominant genotype often does not live to reproductive age. Name one real life situation/disease where this scenario is true.
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19. Explain how genetic variation is maintained in a population despite the lethal result of certain genotypes.
Scenario #5: 20. Explain why you got the allele frequency results that were recorded.
21. What do you predict the frequency of p and q would have been if you continued the simulation for another ten generations? Explain your reasoning.
22. Explain which Hardy-Weinberg condition was broken in this scenario. You must explain your answer to receive credit.
23. This scenario represents a real life situation where the gene pool is dramatically reduced in size. Name three real life situations where this scenario is true. a.
b.
c.
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