Download LAB 5: Breeding Bunnies - Ms Kim`s Biology Class

NAME _________________________________________ DATE ___________________ PER _________
Breeding Bunnies Lab
Sometimes the frequency of alleles changes in a population over a period of time. This means that how often you will
see a particular trait will change also. The purpose of this experiment is to model the changes in gene frequency over
several generations.
In this lab, the dominant allele for normal fur is represented by F (brown bean) and the recessive allele for no fur is
represented by f (white bean). Bunnies that inherit two F alleles or one F and one f allele have fur, while bunnies that
inherit two fs have no fur. The furless rabbit is rarely found in the wild because cold winters are too harsh for the
rabbits, if the rabbits cannot survive the cold, they cannot survive to reproduce.
PART 1 Pre-Lab
1.
Think about the balanced polymorphism article you have just read. Why does the recessive trait continue to
persist in the population if it causes a disease?
2.
What is an example of balanced polymorphism?
3.
Write a hypothesis of how you think the frequency of the alleles (F or f) will change over time for Part 1.
Materials:
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50 brown beans
50 white beans
Paper Bag
3 cups
Penny
Case 1. Selection Against Homozygous Recessive:
In the natural world, not all genotypes have the same rates of survival. The environment may favor some
genotypes while selecting against others. In this Case, we will create a realistic simulation by applying a
selection pressure to the population. In this Case, you will assume that the homozygous recessive individuals
never survive (100% selection against), and that heterozygous and homozygous dominant individuals survive
100% of the time.
Part 1 Procedure:
1. Label the 3 cups FF for the homozygous dominant genotype, Ff for the heterozygous condition, and ff for those
rabbits with the homozygous recessive genotype, respectively.
2. Place the 50 brown and 50 white beans (alleles) in the container and shake up (mate) the rabbits.
3. Without looking at the beans, select two at a time, and record the results on the data table next to "Generation
1." For instance, if you draw one brown and one white bean, place a tally mark in the chart under "Number of Ff
individuals."
4. Continue drawing pairs of beans and recording the results in your chart until all beans have been selected and
sorted. Place the "rabbits" into the appropriate cups: FF, Ff, or ff. (Please note that the total number of
individuals will be half the total number of beans because each rabbit requires two alleles.)
5. The ff bunnies are born furless. The cold weather kills them before they reach reproductive age, so they can't
pass on their genes. Place the beans from the ff container aside before beginning the next round.
6. Count the F and f alleles (beans) that were placed in each of the "rabbit" cups in the first round and record the
number in the chart in the columns labeled "Number of F Alleles" and "Number of f Alleles." (This time you are
really counting each bean). Total the number of F alleles and f alleles for the first generation and record this
number in the column labeled "Total Number of Alleles."
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7. Place the alleles of the surviving rabbits (which have grown, survived and reached reproductive age) back into
the container and mate them again to get the next generation. (Don’t put the ff bunnies back because they are
dead).
8. Repeat steps to obtain generations two through five.
9. Determine the gene frequency of F and f for each generation and record them in the chart in the columns
labeled "Gene Frequency F" and "Gene Frequency f." To find the gene frequency of F, divide the number of F by
the total, and to find the gene frequency of f, divide the number of f by the total. Express results in decimal
form. The sum of the frequency of F and f should equal one for each generation.
PART 1 DATA TABLE
Generation
# of FF
individuals
# of Ff
individuals
# of ff
individuals
# of F
alleles
# of f
alleles
Total # of
alleles
Gene
frequency
of F
Gene
frequency
of f
1
2
3
4
5
In this part of the lab, the homozygous dominant (FF) rabbit will have a greater chance of contracting a disease where
they become deaf and cannot hear predators. Thus, their lifespan is shortened and they may not produce offspring.
PART 2 Pre-Lab
1.
Write a hypothesis of how you think the frequency of the alleles (F or f) will change over time for Part 2.
Case 2: Heterozygous Advantage
From Case 1, it is easy to see what happens to the lethal recessive allele in a population. However, data from
human populations, sometimes show an unexpected high frequency of a deleterious allele in some
populations. Sometimes there is a slight advantage to being heterozygous for a trait rather than homozygous
dominant. So the situation is now more complicated: homozygous recessives are still strongly selected against
and do not survive to reproduce, but now, in addition, homozygous dominants have a lower reproductive rate
than heterozygotes. We will incorporate this fact into our simulation.
Part 2 Procedure:
1. Replace the 50 brown and 50 white beans (alleles) in the container and shake up (mate) the rabbits.
2. Select two beans at a time, and record the results on the data table next to "Generation 1." For instance, if you
draw one brown and one white bean, place a tally mark in the chart under "Number of Ff individuals."
3. Continue drawing pairs of beans and recording the results in your chart until all beans have been selected and
sorted. Place the "rabbits" into the appropriate cups: FF, Ff, or ff. (Please note that the total number of
individuals will be half the total number of beans because each rabbit requires two alleles.)
4. When you get an FF individual, then you need to flip a penny. If you get tails, then they survive. If you get
heads, then they get the deafness disease. They cannot hear a nearby coyote, they get eaten, and they cannot
reproduce.
5. Count the F and f alleles (beans) that were placed in each of the cups in the first round and record the number in
the chart in the columns labeled "Number of F Alleles" and "Number of f Alleles." (This time you are really
counting each bean, but don't count the alleles of the ff and half of the FF bunnies because they are dead.) Total
the number of F alleles and f alleles for the first generation and record this number in the column labeled "Total
Number of Alleles."
6. Place the alleles of the surviving rabbits (which have grown, survived and reached reproductive age) back into
the container and mate them again to get the next generation.
7. Repeat steps to obtain generations two through five.
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8. Determine the gene frequency of F and f for each generation and record them in the chart in the columns
labeled "Gene Frequency F" and "Gene Frequency f." To find the gene frequency of F, divide the number of F by
the total, and to find the gene frequency of f, divide the number of f by the total. Express results in decimal
form. The sum of the frequency of F and f should equal one for each generation.
PART 2 DATA TABLE
Generation
# of FF
individuals
# of Ff
individuals
# of ff
individuals
# of F
alleles
# of f
alleles
Total # of
alleles
Gene
frequency
of F
Gene
frequency
of f
1
2
3
4
5
Lab Questions:
1. Compare the frequencies of the dominant allele to the frequencies of the recessive allele in Part 1? Explain why
this happened.
2. Since homozygous recessives are strongly selected against, would you expect the recessive (a) allele
to be completely removed from the population? In other words, in a large population would it be
possible to completely eliminate a deleterious (or even lethal) recessive allele. Explain.
3. Describe a real-life example of selection against a homozygous recessive genotype.
4. Compare the frequencies of the dominant allele to the frequencies of the recessive allele in Part 2? Explain why
this happened.
5. Do you think the recessive allele will be eliminated in Case 3? Explain.
6. What is the impact of heterozygote advantage to genetic variation in a population? Explain.
7. Describe a real-life example of heterozygote advantage.
8. Imagine we did this experiment one more time. What if there was no advantage or disadvantage to the alleles,
how would the frequencies of the dominant allele to the recessive allele compare?
9. In a real rabbit habitat new animals often come into the habitat (immigrate), and others leave the area
(emigrate). How might emigration and immigration affect the gene frequency of F and f in this population of
rabbits? How might you simulate this effect if you were to repeat this activity?
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10. How are the results of this simulation an example of evolution?
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