Name:__________________________
Period:____
How Does Genetic Drift Effect Allele Frequencies and Variation?
Background:
Genetic drift is the random change in allele frequencies that occurs most commonly in
small populations. Genetic Drift is NOT considered natural selection, because it is random and
not based on fitness! Two types of genetic drift are the founder effect and bottleneck effect. The
founder effect is a change in allele frequencies as a result of the migration of a small subgroup.
The bottleneck effect is when the original population goes through a devastating reduction (such
as a natural disaster) and allele frequencies are changed as a result. Evolution is defined as a
change in allele frequencies over time. Genetic drift can be a strong evolutionary force.
Your Initial Population:
1. You have a cup of 24 M&M's, each M&M represents an allele in the population.
2. Count your alleles and fill-in the data in Table #1
3. Allele Frequency (%) = (one type of allele / all alleles) x 100
TABLE 1: Allele Frequency of Initial Population
COLOR
# of Alleles
Allele Frequency %
Blue
Green
Yellow
Red
Orange
Brown
TOTAL
Modeling the Founder Effect:
1. WITHOUT LOOKING, remove 6 M&Ms at random from the initial population and
place them on the paper towel. Individuals carrying these alleles have left to form a new
population. DONT EAT ANY YET YOU STILL NEED THEM!
2. Record your data into Table #2 for the allele frequencies of your founding and main
population.
3. Return the M&Ms to the cup for the next simulation.
TABLE 2: Founder Effect
COLOR
# of Alleles in
founding
population
# of Alleles in
main
population
Allele
Frequency %
Founding Pop.
Allele
Frequency %
Main Pop.
Blue
Green
Yellow
Red
Orange
Brown
TOTAL
Modeling the Bottleneck Effect:
1. Without looking, remove 18 M&Ms. The individuals carrying these alleles died in a
devastating natural disaster (an onslaught of hungry students).
2. Record the data for the remaining population in Table #3.
TABLE 3: Bottleneck Effect
COLOR
Blue
Green
Yellow
Red
Orange
Brown
TOTAL
# of Alleles
Allele Frequency %
Discussion & Data Analysis
1. How is allele frequency different than genotype?
2. Describe the difference between the founder effect and the bottleneck effect (as defined,
not based on your data).
3. Create a bar graph (final page) to compare your initial, founding, and main population
allele frequencies for each allele color. Use different colors for each population and
include a legend, axis titles, and a title.
Based on your graph,
a. Do the founding and initial populations have the same allele frequencies or
different? Why?
b. Which allele frequencies are more similar to the initial population, the founding
or the main?
c. Explain why or why not your answer to part b is what you would expect:
d. What colors, if any, were in the original population but NOT in the founding
group?
4. Compare the allele frequencies between the initial (Table #1) and surviving population
after a bottleneck (Table #3) with a bar graph (final page).
Based on your graph,
a. Explain why (or why not) there is a difference in allele frequencies between the
initial and surviving population:
5. Explain whether random occurrences cause more dramatic allele frequency changes in
smaller or larger populations:
6. Imagine the founding M&M's moved to a location with dense grass and many bright red
flowers...in the middle of an elementary school campus filled with sugar-seeking youth
who have complete disregard for the 5 second rule.
a. What colors in the founding population (your founding population) would have
highest fitness?
b. What might happen to those alleles (from part a) in the population?
c. Which colors would have low fitness? What would happen to those alleles?
d. Explain whether natural selection is occurring in this population:
7. Explain whether each would lead to a founder effect OR bottleneck effect OR neither:
a. Disease
b. Storm
c. Immigration (new individuals joining population)
d. Searching for food
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