Description
This assignment requires to use a simulation of koi fish in a pond to determine the microevolution. The first step of the assignments is to create a experimental design and the second step is to write a lab report, all the assignment details are attacked into the document.
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LAB: Microevolution and the Hardy-Weinberg Principle
INTRODUCTION
The Hardy-Weinberg Principle states that allele and genotype frequencies will remain unchanged in a population
that is not evolving. Such a population is said to be in Hardy-Weinberg Equilibrium. The Hardy-Weinberg
equation demonstrates the relationship between allele frequencies and genotype frequencies in a population that
is not evolving: p2 + 2pq + q2 =1, where p and q represent two alleles at one locus (e.g., alleles A and B). Each term
in the equation allows us to predict relative frequencies of genotypes using the two allele frequencies: f(AA) = p2,
f(AB) = 2pq, and f(BB) = q2. Because the equation assumes no evolution, it provides a null hypothesis to test
whether a population is evolving and can sometimes help determine which mechanism(s) of evolution may be
acting on the population.
If the relationships between allele and genotype frequencies that one observes in a population are different from
those predicted by the Hardy-Weinberg equation, it is an indication that at least one assumption of
Hardy-Weinberg equilibrium has been violated. Thus, the population is evolving. Each violated assumption is
therefore considered a mechanism of evolution (i.e., a condition that causes allele and/or genotype frequencies in
a population to change from one generation to the next):
1)
2)
3)
4)
5)
Genetic drift
Natural Selection
Migration (gene flow)
Mutation
Assortative (nonrandom) mating
In this lab activity you will demonstrate how three of these mechanisms of evolution cause allele and genotype
frequencies in a population to change over time. The lab uses a simulation of koi fish in a pond to model
microevolution: http://virtualbiologylab.org/ModelsHTML5/PopGenFishbowl/PopGenFishbowl.html. Parameters
that you set prior to each run of the simulator allow you to violate assumptions of Hardy-Weinberg equilibrium in
various ways. The lab is split into two parts:
– Experimental design will be done in class as pairs of students
– Running simulations and interpreting results will done outside of class individually
PART 1: EXPERIMENTAL DESIGN
INSTRUCTIONS: You will use the simulator to determine how three different mechanisms of evolution cause allele
and/or genotype frequencies to change over time in a model population of koi fish. Everyone will test the effects
of genetic drift and natural selection, the third will be your choice. Work with a partner to determine which
parameters you will manipulate to test each question, including the values for each parameter that you change. To
change more than one parameter, copy and paste the necessary fields and number them Parameter 2, Parameter
3, etc. You will NOT need to change Sex Ratio, Mortality Rate, or Brood Size. Please type all your answers directly
into this document using a color other than black.
1) How do different population sizes affect the influence of genetic drift? Genetic drift affects small
populations more than large populations. In small populations, because there are fewer individuals, there
is a higher chance that random events (sudden death or birth) can affect allele frequencies. Genetic drift
is more effective in small populations since there is a small number of individuals that carry out the alleles
through generations. Genetic drift also occurs in large populations, but not as much as small populations
since the random fluctuations in the allele frequencies are less likely to alter the overall genetic makeup
of the population.
Brief description of how you will use the simulator to model this question:
Parameter 1:
_____________________________________________________________________________________
Parameter 1 Default Value:
_____________________________________________________________________________________
Parameter 1 Experimental Value:
_____________________________________________________________________________________
Notice there are two variables that affect population size: Initial Size and Carrying Capacity. Depending on how
you set up this experiment, you could test 1) effects of a consistently small population size, 2) immediate effects
of a genetic bottleneck, and 3) effects of a bottleneck after population size has recovered. You only need to test
one of these three phenomena, but describe here how each would be set up and identify which one you will test:
_____________________________________________________________________________________
_____________________________________________________________________________________
2) How does natural selection affect allele and genotype frequencies in a population over time?
Brief description of how you will use the simulator to model this question:
_____________________________________________________________________________________
Parameter 2:
_____________________________________________________________________________________
Parameter 2 Default Value:
_____________________________________________________________________________________
Parameter 2 Experimental Value:
_____________________________________________________________________________________
3) Create a third question on your own. Choose one of the remaining mechanisms of evolution (gene flow,
mutation, or nonrandom mating) and describe how you plan to test its effects on a koi population.
Brief description of how you will use the simulator to model this question:
_____________________________________________________________________________________
Parameter 3:
_____________________________________________________________________________________
Parameter 3 Default Value:
_____________________________________________________________________________________
Parameter 3 Experimental Value:
_____________________________________________________________________________________
PART 2: LAB PROCEDURE AND ANALYSIS
To answer each question, follow your experimental design to run the simulator. Reset the simulator before each
trial using the icon at the top right (
), and make sure it is paused as you set each parameter. Each reset will
start the population at generation 0. To reset all parameters to their default values you must reload the page in
your browser.
For each treatment (set of initial parameters), run a minimum of 5 trials and allow the simulator to run until it
appears the relatively stable. You may need to experiment with this a few times before deciding on the number of
generaat population size, genotype frequencies, and allele frequencies becomtions needed for each treatment.
For each of your three research questions, report the following:
1) Introduction – Write one or two short paragraphs that provide context and/or the purpose for the lab.
This section should be brief and should demonstrate that you understand how/why the lab is relevant to
what we’re learning in class.
2) Data & Results – Reproduce the table shown under “Data Collection” of the simulator, but create a
column for each trial run. Tables should be labeled/titled Table 1, Table 2, etc.
3) Analysis – Use your results and to answer the research question. Be sure to cite quantitative evidence
from your results tables. Calculating mean values and reporting the range of values obtained around that
mean may be useful for some or all of the questions, but that’s up to you to decide and no formal
statistics tests are required. The analysis should be presented in paragraph form. Remember CER: claim,
evidence, reasoning – don’t try too hard to fit everything rigidly into this formula, but DO be aware of
when you are making a claim supported by evidence as opposed to providing reasoning based on your
knowledge of population genetics learned this unit. Your writing should demonstrate that you understand
the difference.
*Make sure your lab report is well-organized.*
LAB REPORT
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