Natural Selection Virtual Lab
http://mhhe.com/biosci/genbio/virtual_labs/BL_12/BL_12.html
Background:
In this experiment, you will investigate a simulated model of natural selection of an organism in four different environments (Rocky, Desert, Grasslands, Urban).
The simulation represents the effect of predation on natural selection. In the simulation, a predator finds certain phenotypes of the prey more easily in those
environments where they do not blend in. By placing pressure on specific phenotypes to survive, a change in the frequency of the alleles that produce these
phenotypes will occur. Natural selection can significantly alter the genetic balance of a population’s gene pool over time and evolution can be described as the
change in allelic frequencies of a gene pool over time. This can lead to the evolution of a new species. In this simulation, the initial allelic frequencies will tell
you the number of organisms of each genotype in the environment of the parent (first) generation. After natural selection occurs, the survivors will then
reproduce and show how natural selection has affected allelic frequencies. The survival and reproduction will continue for 5 generations.
Essential Vocabulary:
Gene – one set of instructions for an inherited trait
Trait – genetically determined characteristic that can be passed from parent to offspring through genes
Genotype – the entire genetic makeup of an organism; also the combination of genes for one or more specific traits. The simulated environments in this
experiment have three genotypes:



AA = yellow ants
Aa=green ants
aa=grey ants
Allele – One of the alternative forms of a gene that governs a characteristic, such as hair color. Alleles can be dominant or recessive. Dominant alleles are
shown with a capital letter, recessive alleles are shown with a lowercase letter.
Phenotype- an organism’s appearance or other detectable characteristic. Not all phenotypes are visible. For example, a plant may be drought resistant and this
trait would only be detectable in a dry environment.
Instructions:
1.
2.
3.
4.
Select the environment and appropriate allele frequency at the top.
Click through the generations and record the number of each allele before and after natural selection occurs.
Click reset to choose a new environment and allele frequency
Record your data for all four allele combinations and note which color ant is the “Best Survivor”
Conclusion Questions:
1.
Did either allele “A” or “a” disappear from the populations you studied? Explain.
Did either allele ever reach zero? If so, what
environment and which generation?
2. Did the effect of natural selection vary with different starting allele frequencies in identical environments? Explain.
Pick one environment (rocky)
the number of each allele?
3.
Compare before and after for both charts. What are you noticing that happens with
A population in which the frequency of alleles remains the same over generations is said to be in genetic equilibrium. Describe one mechanism by which
a populations' genetic equilibrium can be disrupted and result in the process of evolution.
Equilibrium means equal. What has to happen
in order for the allele frequency to change from being equal to forcing evolution to happen? Anotherwords,
equilibrium has been thrown off
4. In which of the simulated environments do individuals of the genotype Aa (green ants) survive best?
5. In which of the simulated environments do individuals of the genotype aa (grey ants) survive best?
6. Which environment represents a type of natural selection that stabilizes the allele frequencies of the population? How do you know? Another words,
which type of environment allows all three allele frequencies (three different color ants) to survive
Rocky Environment
AA
Aa
aa
Yellow
Green
Grey
Generation 1
Generation 2
Generation 3
Generation 4
Generation 5
Best Survivor
4
2
1
0
32
21
19
13
64
77
Grasslands Environment
AA
Aa
aa
Yellow
Green
Grey
Urban Environment
AA
Aa
aa
Yellow
Green
Grey
A=0.4
a=0.6
Desert Environment
AA
Aa
aa
Yellow
Green
Grey
Grasslands Environment
AA
Aa
aa
Yellow
Green
Grey
Urban Environment
AA
Aa
aa
Yellow
Green
Grey
64
77
Rocky Environment
AA
Aa
aa
Yellow
Green
Grey
Generation 1
Generation 2
Generation 3
Generation 4
Generation 5
Best Survivor
A=0.2
a=0.8
Desert Environment
AA
Aa
aa
Yellow
Green
Grey
Rocky Environment
AA
Aa
aa
Yellow
Green
Grey
A=0.5
a=0.5
Desert Environment
AA
Aa
aa
Yellow
Green
Grey
Grasslands Environment
AA
Aa
aa
Yellow
Green
Grey
Urban Environment
AA
Aa
aa
Yellow
Green
Grey
Rocky Environment
AA
Aa
aa
Yellow
Green
Grey
A=0.6
a=0.4
Desert Environment
AA
Aa
aa
Yellow
Green
Grey
Grasslands Environment
AA
Aa
aa
Yellow
Green
Grey
Urban Environment
AA
Aa
aa
Yellow
Green
Grey
Generation 1
Generation 2
Generation 3
Generation 4
Generation 5
Best Survivor
Generation 1
Generation 2
Generation 3
Generation 4
Generation 5
Best Survivor