Genetic Drift Simulations
[Year]
Background
Genetic drift is a change in an allelic frequency in a given population due to random sampling. Alleles
can disappear completely. In this lab, you will be simulating two types of genetic drift. Bottleneck
Effect occurs when a population undergoes a drastic reduction in size (volcano eruption or hurricane).
Founder Effect occurs when a small group of individuals become separated from the larger parent
population (migration). Both of these happen as a result of chance.
You will be predicting the type of change you expect to occur based on your understanding of genetic
drift.
PART 1—BOTTLENECK EFFECT
Procedure






With your partner, establish a starting population of 50 individuals (50% for each allele). You
should have a total of 100 beads.
Without replacement, choose 5 individuals (10% of population), picking up 2 alleles at a time.
Determine the new allelic frequencies and record on the data table.
Establish a new population of 50 individuals using your new allelic frequencies.
Repeat for a total of 4 generations.
Summarize your results in the space provided for you. You will write a summary separate from
your partner. I WANT ONE SUMMARY PER PERSON.
PART 2—FOUNDER EFFECT
Procedure






Establish your starting population of 50 individuals, your choice of a starting allelic frequency.
Record your starting frequency on the data table (Generation 0).
Without replacement, randomly select 5 individuals (10% of the population), picking 2 alleles at
a time.
Record your genotypes and number of each allele for the new population.
Re-establish the population back to 50 individuals using your new allelic frequencies.
Repeat for a total of 4 generations.
Genetic Drift Simulations
[Year]
BOTTLENECK EFFECT DATA TABLE
Generation
AA
Observed Genotypic Frequency
Aa
aa
Observed Allelic Frequency
A
a
0
1
2
3
4
FOUDNER EFFECT DATA TABLE
Generation
Observed Genotypic Frequency
AA
Aa
aa
Observed Allelic Frequency
A
a
0
1
2
3
4
Discussion Questions for Bottleneck Effect
Answer the following questions on a separate sheet of paper.
1. How many generations did you simulate?
2. Did one allele go into fixation? Which allele?
3. Compare your results with four other teams. Did the same allele go to fixation? If not, how
many became fixed for the dominant allele and how many for the recessive allele?
4. How might your results have differed if you had started with a different allelic frequency?
5. Since only chance events are responsible for the change in gene frequency, would you say that
evolution has occurred? Explain.
Discussion Questions for Founder Effect
1.
2.
3.
4.
Describe your change in the allelic frequencies.
Compare your final allelic frequencies with those of the starting population.
Formulate a general summary statement or conclusion.
Would you expect your results to be the same if you had chosen a different starting allelic
frequency? Explain.