Download Bottlenecks and Founder Effects

AP Biology: Genetic Drift Simulation
Name:
Period:
Target III: Describe the two main causes of microevolution: genetic drift (bottleneck effect &
founder effect) and natural selection. Text Reference: 23.3
Pre-lab Questions: Read the procedures before you answer the pre-lab questions. This may be
checked, collected, or possibly be used on a pre lab quiz.
1.
What is meant by a change in allelic frequency?
2.
Define evolution in terms of allelic frequency.
3.
What three mechanisms alter allele frequencies?
4.
Define genetic drift.
5.
What is the founder effect and how is it related to genetic drift? Give an example.
6.
What is the bottleneck effect and how is it related to genetic drift? Give an example.
7.
Could genetic drift lead to evolution of a population? Explain.
8.
Predict: Will the effects of genetic drift on the gene pool differ with sample size? Explain.
9.
Look over the procedures: Why does the teacher want you to take random samples? Would be
illustrating genetic drift if you selected the individuals non-randomly?
Genetic Drift Simulation
Background:
In addition to natural selection, one of the mechanisms leading to evolution is genetic drift. Genetic drift is the
change of allelic frequencies in the gene pool due to random sampling. This simulation will explore how
sample size can influence the effect on genetic drift on the gene pool using different types of beans to
represent individuals in the population.
Vocabulary
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Genetic drift
Gene pool
Allele (allelic frequency)
Evolution
Speciation
Genetic Variation
Materials
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100 beans; 30 kidney, 40 black, and 30 pinto
One Ziploc bag (this will be used to hold your beans)
Safety
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Choking hazard: Do not put the beans in your mouth! Do not eat the beans!
Procedure
 You will be working in small groups of 3-4 people (working at a single table).
 Each group will do two simulations each with three separate trials.
 You will need a bag filled with your bean population. This population will consist of 100 beans
as described in the materials section.
 Read the procedure carefully before starting your trials.
Simulation I (Large sample):
Phenotype
(Color)
Original
Population
#
Ratio(%)
Beans
Trial #1
#
Beans
Ratio(%)
Trial #2
#
Beans
Ratio(%)
Trial #3
#
Beans
Ratio(%)
Bean Totals =
1. Count out the numbers of each phenotype in your large population (bag received from the teacher).
Determine your phenotypic (trait= “color”) ratio (depict your ratios of each phenotype as percentages).
2. Randomly take a sample from the population (roughly 40-50).
3. Determine the ratio in the sample- did any of the allelic frequencies change?
4. Repeat three times (after returning the sample back to your main population to ‘restock’ each time).
Simulation II (small sample):
1. For simulation II follow the same procedures as in simulation I above, but use a smaller sample size of 10 beans.
2. Record your data in the table below.
Phenotype
(Color)
Original
Population
#
Ratio(%)
Beans
Trial #1
#
Beans
Ratio(%)
Trial #2
#
Beans
Ratio(%)
Trial #3
#
Beans
Ratio(%)
Bean Totals =
Post-lab Questions
1. Compare your results from simulation I and II. Did genetic drift have more of an effect on the allelic
frequencies in the larger or smaller samples?
2. An environmental change gave one phenotype an adaptive advantage over the others, increasing its
fitness. This would cause a shift in allelic frequencies as the fittest beads are best able to survive and
reproduce. Would this be an example of genetic drift? Why or why not?
3. Could genetic drift eventually lead to speciation? Explain why or why not.