Genetic Drift Lab:
Founder Effect vs. Bottleneck Effect
Background:
Genetic drift is defined as the random change in allele frequencies that occurs in small populations. It is not due
to natural selection. Genetic drift is strongly tied to population size and becomes important in situations where a
small segment of an original population splits off or becomes isolated from the parent population. A change in allele
frequencies as a result of this migration of a small subgroup of a population is known as ‘founder effect’. Other
times this process occurs when the original population undergoes a devastating population reduction (i.e. by natural
disaster) and the allele frequencies are changed as a result. This is referred to as the ‘bottleneck effect’.
Evolution at the population level is defined as a change in allele frequency over time. This lab will demonstrate how
genetic drift can be a strong evolutionary force in certain situations. We will see that a smaller population size can
show a much more dramatic shift in allele frequencies over time due to these two events.
Initial Population:
1. Pick up a cup of 24 Plain M&M’s and a paper towel; this represents the original population of a group of
organisms known as Candus spectacularus. Each colored M&M represents 1 allele found in the population.
Note that there are 6 possible alleles represented in this population (multiple alleles).
2. Count the alleles in your initial population and fill-in the data in Table#1.
3. Use the following math formula to calculate Allele Frequency:
Allele Frequency (%) = total # of each allele X 100
total # of all alleles
Founder Effect:
4. WITHOUT LOOKING remove 6 M&M’s from the cup and place them on the paper towel; this represents
the founding group. The founding group has left the original population to start a new population. How did
this emigration by the founding group affect the allele frequencies seen in this new population? (Discuss).
Record all the data for Table #2.
5. Now, put the 6 M&M's back into the cup. We will now study the bottleneck effect on this original
population.
Bottleneck Effect:
6. Without looking, remove 18 M&M’s. This removal represents a natural disaster that has hit the Candus
spectacularus population. A hurricane has wiped out most of the members in this population. Only 3
individuals remain, each having 2 alleles (6 alleles). What do the allele frequencies look like after this
disaster? (Discuss). Record all the data for Table #3.
Discussion Questions:
*Answer in complete sentences on your own paper.
1.
2.
3.
4.
How is an allele frequency different than a genotype?
Define genetic drift.
Define founder effect.
Compare table #1 and table #2. Compare allele frequencies for each allele represented in the original
population with those represented in the founding population (i.e. the red allele might have been 50% in the
founding group while it was only 16% in the original population). Use the table for these comparisons.
Color
Allele Freq in original pop.
Allele Freq in founding pop.
Blue
Green
Yellow
Red
Orange
Brown
5.
6.
7.
8.
What colors (if any) in the original population are NOT represented in the founding group?
When you compare the allele frequencies for each color, are they the same for the original population and
the founding population? Why? (Use your notes to help you describe what’s causing this change in allele
frequencies).
Define bottleneck effect.
Compare table #1 and table #3. Compare allele frequencies for each allele represented in the original
population with those alleles represented in the population after the hurricane (after the bottleneck
event). Use the table for these comparisons.
Color
Allele Freq in original pop.
Allele Freq after bottleneck
Blue
Green
Yellow
Red
Orange
Brown
When you compare the allele frequencies for each color, are they the same for the original population and
the surviving population? Why?
10. Is there more of a dramatic change in allele frequencies when alleles change in larger populations or when
alleles change in smaller populations? Explain.
11. Let's assume that the M&M's are praying mantises (green bugs). A group of mantises have gone on strike
and moved to a new environment, which consists of lots of greenery with many bright red flowers. Birds
love to eat praying mantises.
a. Which colors in the founding population (blue, green, yellow, red) would have a higher fitness level in
this new environment? Why?
b. What might happen to those alleles in the population (increase or decrease)?
c. Which colors in the founding population (blue, green, yellow, red) would have a lower fitness level in
this new environment? Why?
d. What might happen to those alleles in the population (increase or decrease)?
e. Is natural selection acting on this founding population? Explain.
9.
12. From the list below indicate whether it will lead to a founder effect or a bottleneck effect. Explain.
a. Disease
b. Immigration (organisms moving into an existing population)
c. Storm
d. Searching for food
13. Calculate percent change of allele frequencies after each event (founding effect and bottleneck) by using
the following math formula:
% change = Allele frequency after bottleneck – Allele frequency of initial population X 100
Allele frequency of initial population
Color
% Change after Bottleneck
Blue
Green
Yellow
Red
Orange
Brown
% Change after Founder
Effect
14. On the back of your data table create 2 bar graphs (for bottleneck and founder effect) of the percent
change of each allele. Be sure to include a proper title, labels, and units.
15. Compare your graphs with another group. Describe these comparisons.
DATA SHEET- Genetic Drift Lab:
Founder Effect vs. Bottleneck Effect
Table 1: Allele Frequency in the Gene Pool for the Initial Population of Candus spectacularis
Color
# of Alleles Frequency of Alleles (%)
Blue
Green
Yellow
Red
Orange
Brown
TOTAL
Table 2: Allele Frequency for the Founding Group
Color
# of Alleles Frequency of Alleles (%)
Blue
Green
Yellow
Red
Orange
Brown
TOTAL
Table 3: Allele Frequency of Surviving Population after Bottleneck Event
Color
# of Alleles Frequency of Alleles (%)
Blue
Green
Yellow
Red
Orange
Brown
TOTAL