Download Natural Selection Simulation Name: Introduction: Natural Selection

Natural Selection Simulation
Introduction:
Name: _______________________________
Natural Selection is often referred to as “survival of the fittest,” but “fittest” doesn’t always mean the same thing. Fitness is
defined as an organism’s ability to survive and reproduce. Over many generations natural selection acts on populations. All
populations share what is known as a gene pool. Due to natural selection, over time the versions genes that improve fitness increase
in the gene pool, and those that hurt fitness decrease. The different versions of genes are called alleles. How often one allele occurs
compared to others is called relative allele frequency. It is important to remember that fitness is directly related to the type of
environment an organism lives in. Today you will do a simulation to show the affect that natural selection and a changing
environment can have on the allele frequencies of a population.
Pre-lab:
1. By reading the introduction above, define the following vocabulary terms:
Natural Selection:
Fitness:
Alleles:
Relative Allele Frequency:
Go to the following website:
http://www.mhhe.com/biosci/genbio/virtual_labs/BL_12/BL_12.html
We are going to be studying a population of insects focusing on the gene which codes for the color of these
organisms. This is a case in incomplete dominance and the genotypes and phenotypes are as follows:
AA= Yellow
Aa= Green
aa= Grey
2. If you cross a two green individuals what are the probable genotypic and phenotypic ratios in of the
offspring?
Procedure:
1. You will be choosing 2 environments to test. We will be looking at how natural selection changes a population
over 5 generations.
2. The bar at the top right of the screen shows the relative allele frequencies for the alleles A and a. Set it to
A=0.5 and a = 0.5 for the beginning of each simulation. This means that our population will start off with equal
percentages of A and a in the gene pool.
3. Use the bar on the top left to select an environment. You can choose any two that you want.
4. When you are ready to start click on “Generation 1.” Record how many of each phenotype/genotype from the
“before” column in your data table. Then click “natural selection.”
5. After natural selection has acted upon your population you will see the allele frequencies change. Click
“generation 2” and record the new numbers that are in the “before” column into your data table
6. Repeat for all five generations.
7. Choose a new environment and repeat all steps.
Results:
Table 1: Environment: _______________________________________
Number of Individuals
Generation 1
Generation 2
Generation 3
Generation 4
Generation 5
AA (Yellow)
Aa (Green)
aa (Grey)
Starting Allele Frequency: ____________________
Ending Allele Frequency: ____________________
Table 2: Environment: _______________________________________
Number of Individuals
Generation 1
Generation 2
Generation 3
Generation 4
Generation 5
AA (Yellow)
Aa (Green)
aa (Grey)
Starting Allele Frequency: ___________________
Ending Allele Frequency: ____________________
*Create a line graph for each data table. Each graph will have a line for each phenotype/genotype so make sure that you include a
key telling which line is which.
Discussion Questions:
1. What environment did you choose first, and how did the population change over the five generations?
2.
What environment did you choose second, and how did the population change over the five generations?
3.
Based on what you know about genetics, why didn’t some of the colors disappear completely when their fitness was
low? (hint: think about pre-lab question 2)
4.
Did any individuals actually change during this simulation?
5.
In this simulation we were focusing on a prey species. Describe how you think natural selection could also affect
predators.
6.
In your own words, what is natural selection?