Download A Mutation Story - Harrison High School

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Title: Allele Frequencies and Sickle Cell Anemia Lab
Background Information:
Watch the 4 minute video called “ Mutation Story” to learn some background
information for today’s lab. Answer the following questions:
1. What causes Malaria?
2. What carries this and infects humans?
3. What does malaria do to red blood cells in a human?
4. What causes Sickle Cell Anemia?
5. What is special about people with one copy of the sickle cell mutation?
6. Show a cross of two parents that are heterozygous for the sickle cell trait.
Let “A” represent those with the normal allele and “S” represent the sickle
cell allele.
A
S
A
S
7. Which genotype would die if they got malaria. __________ What %
would that be? ___________
8. Which offspring will have sickle cell anemia and probably die an early
death? _________
9. Which offspring will be resistant to malaria? __________ What %
would that be? ________
More info: Allele frequency refers to how often an allele occurs in a population.
Allele frequencies can change in a population over time, depending on the
“selective forces” shaping that population. Predation, food availability, and
disease are all examples of selective forces. EVOLUTION OCCURS WHEN ALLELE
FREQUENCIES CHANGE IN A POPULATION.
In this activity, the gene pool exists in a region of Africa that is infested with
malaria. We are simulating the effects of a high frequency of malaria on the
allele frequencies of a population.
Hypothesis:
What do you think will happen to the frequencies of the A & S alleles as a result
of the presence of malaria? Will the frequency of A increase or decrease? What
about S? Explain your reasoning.
Materials: 75 red beans, 25 white beans, 5 containers, coin
Procedure:
1. Together with your lab partners, obtain the materials for the lab. Count
your beans. The red beans represent gametes carrying the A allele and
the white beans represent gametes carrying the S allele. Obtain your 5
labeled containers. They are labeled as “AA, AS, SS, Non-surviving alleles,
& gene pool”.
2. Place the beans in the gene pool container and mix the beans up.
3. Simulate fertilization by PICKING OUT two “alleles” (beans) without
looking.
4. For every two beans that are chosen from the gene pool, another person
will flip a coin to determine whether that individual is infected with malaria.
5. Using the table below, the coin flipper tells the bean picker in which
container to put the beans.
Genotype
Phenotype
Malaria (Heads)
AA (red/red)
No sickle cell
disease. Malaria
susceptibility.
No sickle cell
disease. Malaria
resistance
Sickle Cell Disease
Live: Place in AS
Live: Place in AS
Die: Place in Nonsurviving
Live for a brief
time, place in SS
AS (red/white)
SS (white/white)
Not infected
(Tails)
Die: Place in Non- Live: Place in AA
surviving
6. Repeat steps 3-5 until all the beans in the gene pool are used up.
7. At the end of the round, count the number of individual red beans (A
alleles) and white beans (S alleles) in the containers labeled AA and AS.
These individuals survive to reproduce. RECORD those numbers in the F1
TOTAL SURVIVNG ALLELES table. Put them in the gene pool again after
you count them.
8. Because SS individuals do not survive to reproduce, move all beans from
the SS alleles container into the Non-surviving alleles container.
STOP AFTER ONE GENERATION. CHECK WITH YOUR TEACHER BEFORE
GOING ON.
9. Repeat the procedure for the F2 generation. Record your results in the F2
TOTAL SURVIVING ALLELES table.
F1 TOTAL SURVIVING ALLELES
Number of A (Red) alleles surviving
(count out of AA & AS containers)
Number of S (White) allele surviving
(count out of AS container)
F2 TOTAL SURVIVING ALLELES
Number of A (Red) alleles surviving
(count out of AA & AS containers)
Number of S (White) alleles surviving
(count out of AS container)
Class Results
Parents
A
F1
S
A
F2
S
A
S
Class Total
Allele
Frequency
Analysis Questions:
1. What do the red & white beans represent in this simulation?
2. What does the coin represent?
3. What do you think “allele frequency” means and how are allele
frequencies related to evolution?
4. What are “selective forces” in this simulation (forces that change the allele
frequency)?
5. What was the general trend you observed for allele A over three
generations (increase/decrease)?
6. What was the general trend for allele S over time? Was your hypothesis
supported?
7. Do you anticipate that the trends will continue for many generations?
Why or why not?
8. Since few people with sickle cell anemia (SS) are likely to survive to have
children of their own, why hasn’t the mutant allele (S) been eliminated?
(Hint: what is the benefit of keeping it in the population?)
9. Why is the frequency of the sickle cell allele so much lower in the US than
in Africa?
10. Scientists are working on a vaccine against malaria. What impact might
the vaccine have in the long run on the frequency of the sickle cell allele
in Africa? (Increase/decrease and why?)