Lab Handout: Population Genetics of Koi Fish
Click the link below to get started.
http://virtualbiologylab.org/ModelsHTML5/PopGenFishbowl/PopGenFishbowl.html
Start by clicking “Background Information.”
Read the presented information to answer the following 20 questions:
1. Define biological evolution.
2. What is the difference between microevolution and macroevolution?
3. What are the five conditions that must be met for the proportions of alleles to not change (Hardy-
Weinberg Equilibrium)
1
2
3
4
5
4. What are the five evolutionary mechanisms? Give a brief description of each.
Mechanism
1
2
3
4
5
Description
5. What are some examples of selective breeding?
6. What are the three varieties of koi?
Part 1: Population in Hardy-Weinberg Equilibrium
Click the “Home” icon to go back to the main menu and click on “Run Experiments.”
First, we will work with the default parameters. This default population is in Hardy-Weinberg equilibrium.
7. Before switching over to the data collection tab, calculate the following variables. The frequency of the
dominant allele (p) = 0.5 and the recessive allele (q) = 0.5. (p + q = 1)
Frequency of homozygous dominant genotype (RR)
Frequency of heterozygous genotype (Rr)
Frequency of homozygous recessive genotype (rr) =
p2 =
2pq =
q2 =
8. Click “To Data” and compare your genotype predictions to the frequencies in the model. Allow the
simulation to run for 100 generations (press the fast forward button to speed up the simulation and you
can also pause it). What are the frequencies?
Frequency of dominant allele (R) =
Frequency of recessive allele (r) =
Frequency of homozygous recessive genotype (rr) =
Frequency of heterozygous genotype (Rr) =
Frequency of homozygous dominant genotype (RR) =
9. Reset the simulation by hitting the blue reset button in the top right. Return to the design page, and
now change the initial ‘R’ Allele proportion to 0.3. Calculate the following (see H-W Equation):
Frequency of dominant allele (R)
p=
Frequency of recessive allele (r)
q=
Frequency of homozygous recessive genotype (rr)
q2 =
Frequency of heterozygous genotype (Rr) 2pq =
Frequency of homozygous recessive genotype (RR) = p2 =
10. Run the simulation through 100 generations. What are the frequencies now?
Frequency of dominant allele (R)
p=
Frequency of recessive allele (r)
q=
Frequency of homozygous recessive genotype (rr)
q2 =
Frequency of heterozygous genotype (Rr) 2pq =
Frequency of homozygous dominant genotype (RR) =
q2 =
11. Is this population in Hardy-Weinberg Equilibrium? How do you know? Explain these results.
12. Will this population ever reach equilibrium? Why or why not?
Part 2: Selection and Fitness
Relative Fitness is the survival rate of a genotype (or phenotype)
relative to the maximum survival and/or reproductive rate of other
genotypes in the population. It is a number between 0 and 1.
Investigation 1: Selection for Spotted
You will investigate a scenario where the spotted phenotype is
advantageous because koi fish with a spotted pattern are less likely to
be seen by predators. Set your simulation to the following parameters:
Carrying capacity: 200
Initial ‘R’ Allele Prop: 0.5
Relative genotype fitness of rr: 0.7
Relative genotype fitness of RR: 0.7
Click the “Reset” button to begin data collection.
13. Allow the simulation to run for at least 100 generations, and then record your data in the table below:
Proportion of rr Genotype after 100 generations
Proportion of Rr Genotype after 100 generations
Proportion of RR Genotype after 100 generations
14. What is meant by “FITNESS” in this scenario?
Investigation 2: Selection Against White
Now, you’ll investigate a scenario where selection is against a particular phenotype (in this case, perhaps the
white phenotype is disadvantageous because those fish are easily seen by predators). Set your simulation to
the following parameters:
Relative genotype fitness of rr: 0.3
Relative genotype fitness of Rr: 1
Relative genotype fitness of RR: 1
15. Click the reset button to begin data collection. Allow the simulation to run for at least 100 generations,
and then record your data in the table below:
Proportion of rr Genotype after 100 generations
Proportion of Rr Genotype after 100 generations
Proportion of RR Genotype after 100 generations
16. We reasonably expect there to be no white fish because of the selection, but the frequency of r may not
be zero, even if there are no white fish. Why not?
17. It is likely that there were sometimes no white fish for a period, but then a few returned a few
generations later. What might cause this?
18. In population genetics, fixation is the change in a gene pool from a situation where there exist at least
two variants of a particular gene (allele) in each population to a situation where only one of the alleles
remains. The gene has become “fixed.” Describe how this might happen in the koi population.
19. Summarize the effect of natural selection on the evolution of populations. Use the term “fitness” in your
explanation.
20. The simulator also allows you to adjust “assortative mating.” Change the strength of this parameter to 1
and run some simulations. Describe what happens and propose a definition for assortative mating.