Hardy-Weinberg Lab (“The Mating Game”)
How do you measure Evolution?
Allele Frequencies
Genotype Frequencies
p+q=1
p2 + 2pq + q2 = 1
Introduction
In this experiment you and your classmates will represent an entire breeding population. Each member of the
class will receive four cards. Two cards have a and two cards have A, all possible alleles for a gene. The four
cards represent the products of meiosis. Each “parent” contributes a haploid set of chromosomes to the next
generation. Each simulation has a unique set of rules, so follow accordingly. You will track your own set of
alleles for each generation and contribute that information to a class data set for analysis.
Case I: Ideal Hardy Weinberg Populations
Methods
1.
2.
3.
4.
5.
6.
You begin this simulation as a heterozygote.
Begin simulation by walking around the room. Pick a mate at random and show them your mating dance.
Once your mating request is accepted, shuffle your cards behind your back and take the card on top to contribute to the
production of the first offspring. Your partner should do the same.
Put the two cards together. The two cards represent the alleles of the first offspring. One of you will assume the genotype of
this child and record that in your data table for your F1. Shuffle again to determine the genotype of the 2nd offspring, and the
other parent will record that new genotype in their F1.
You will assume the genotype of the offspring you chose (1 st child or 2nd child) for the next round of mating, so make sure
your allele cards reflect what you are able to contribute when you mate again.
Repeat steps 2-5 for the next set of generations, recording your genotype after each round.
Results
Individual Data
Case I: Ideal Hardy-Weinberg Population
My initial
genotype
F1
F2
F3
F4
F5
Ideal
Hardy-Weinberg
Generation
AA
Aa
aa
Number of Surviving alleles
Total
individuals
A
a
p=
q=
p=
q=
Class Data
Initial Class
Frequencies
F1
F2
F3
F4
F5
Final Class
Frequencies
Surviving Genotypes
Total
alleles
Case I: Ideal Hardy Weinberg Populations
Debrief
1. What does the Hardy Weinberg equation predict for the new p and q for this simulation?
2. Do the results you obtained in this simulation agree? If not, why not?
3. What major assumptions were not strictly followed in this simulation? Consider what “ideal Hardy-
Weinberg conditions” means.
Case II: Selection
In this case you will modify the simulation to make it more realistic. In the natural environment, not all genotypes have
the same rate of survival; that is, the environment might favor some genotypes while selecting against others. An example
is the human condition, sickle cell anemia. It is a disease caused by a mutation on one allele, homozygous recessives
often die early. For this simulation, you will assume that the homozygous recessive individuals never survive, and that
heterozygous and homozygous dominant individuals survive ever time.
Methods
Once again start with your initial genotype (Aa) and produce fertile offspring as in Case I. There is an important change in this
experiment. Every time an offspring with the genotype aa is produced it dies. The parents must continue to reproduce until two
fertile offspring are produced. As in Case I proceed through five generations, but select against the aa every time.
Individual Data
Results
Selection
Generation
Surviving Genotypes
Aa
aa
Total
individuals
Number of Surviving alleles
A
a
Total
alleles
p=
q=
p=
q=
Class Data
Initial Class
Frequencies
F1
F2
F3
F4
F5
Final Class
Frequencies
AA
Case II: Selection
My initial
genotype
F1
F2
F3
F4
F5
Case II: Selection
Debrief
1. Compare the new frequencies of p and q to the initial frequencies in Case I. initial:
new:
How has the allele frequency of the population changed? Why?
2. Predict what would happen to the frequencies of p and q if you simulated another five generations.
3. In a large population, would it be possible to completely eliminate a deleterious recessive allele? Explain.
Case III: Heterozygote Advantage
From Case II, it is easy to see that the lethal recessive allele rapidly decreases in the population. However in a
real population there is an unexpectedly high frequency of the sickle cell allele in some populations. Case II did
not accurately depict a real situation. In the real world heterozygotes have an advantage over homozygous
dominant organisms. This is accounted for in Case III.
Methods
In this case everything is like Case II except if your offspring is AA, flip a coin. If it is heads the individual dies, if it is tails it lives. The
genotype aa never survives. Once again simulate five generations, starting with the initial genotype form Case I.
Individual Data
Results
Heterozygote
Advantage
Generation
Case III: Heterozygote Advantage
My initial
genotype
F1
F2
F3
F4
F5
Surviving Genotypes
AA
Aa
aa
Number of Surviving alleles
Total
individuals
A
a
p=
q=
F1
F2
F3
F4
F5
Final Class
Frequencies
p=
q=
Class Data
Initial Class
Frequencies
Total
alleles
Case II: Heterozygote Advantage
Debrief
1. Explain how the changes in p and q frequencies in Case II compare with Case I and Case III.
2. Do you think the recessive allele will be completely eliminated in either Case II or Case III?
3. What is the importance of heterozygotes, the heterozygote advantage, in maintaining genetic variation in
populations?
Case IV Genetic Drift
In each generation, some individuals may, just by chance, leave behind a few more descendants (and genes,
of course!) than other individuals. The genes of the next generation will be the genes of the "lucky" individuals,
not necessarily the healthier or "better" individuals. It can be the result of a natural disaster (bottleneck effect) or
a new colony is established by only a few members of an original population. This case will simulate genetic
drift in an isolated population.
Methods
Resume the original set of heterozygotes in the entire class. Then, randomly divide into 3 groups to simulate several smaller
“populations” so that individuals from one isolated “population” do not interact with individuals from another population. Go through
5 generations as you did for Case I.
Individual Data
Results
Case IV: Genetic Drift
My initial
genotype
F1
F2
F3
F4
F5
Genetic Drift
Generation
AA
Case IV: Genetic Drift
Debrief
Compare allele frequencies (Case I initial to this F5).
What do your results indicate about the importance of
population size as an evolutionary force?
Surviving Genotypes
Total
Aa
aa
Number of Surviving alleles
Total
A
a
individuals
p=
q=
p=
q=
Class Data
Initial Class
Frequencies
F1
F2
F3
F4
F5
Final Group
Frequencies
alleles