Natural Selection and Allele Frequency
Background: Evolution can be described as the change in allele frequencies of a gene pool over
time. Natural Selection can place pressure on specific phenotypes and cause a change in the frequency
of the alleles that produce phenotypes. In this activity, you will simulate the effects of eagle predation
on a population of rabbits, where GG represents the homozygous dominant condition for brown fur,
Gg is the heterozygous condition for brown fur, and gg represents the homozygous recessive
condition for white fur.
Procedure:
Pinto (brown) beans = G
Navy (white) Beans = g
1. Count out 50 Pinto beans and 50 Navy beans. Place them into a paper bag.
2. Shake the bag. Remove 2 beans. These beans represent the rabbit’s genotype. Set the pair aside, and
continue to remove 49 more pairs. NO WHINING!!!! As you remove the beans, place them into two
columns: Brown Fur (genotypes GG and Gg) and White Fur (genotype gg).
3. Examine the columns. Remove 25% of the brown rabbits and 100% of the white rabbits. These
numbers represent a random selection pressure on your rabbit population. If 25% of your brown
rabbits is a fraction, remove a whole rabbit.
4. Count the number of Pinto and Navy beans remaining. These numbers represent the number if G
and g alleles remaining in your population after eagle predation. Record this number on your data
table.
5. Calculate the percentage of G alleles (Pinto beans) remaining by dividing the number of G’s by the
total number of alleles (both types of beans) remaining. Record this number on your data table and
repeat calculations for g alleles (Navy beans).
6. To figure out the frequencies, simply convert your percentages into fractions.
7. Begin the next generation with 100 beans using the ratio calculated in Step 5. Example: If in
Generation 1 there was 64% Pinto beans and 36% Navy beans, then you would start the second
generation with 64 Pinto beans and 34 Navy beans…it adds up to 100.
8. Continue collecting data in this manner for 5 generations.
9. Finish by answering the analysis questions and graphing your data. (Plot the frequency of the allele
on the y-axis and the number of the generation on the x-axis. Use a different color pencil for each
allele. Use the space provided…in other words, DON’T MAKE YOUR GRAPH TOO SMALL!!!)
Extra Credit Opportunity
On a separate sheet of GRAPH PAPER, draw a new G and g allele table and a new graph (just like the
ones in your lab report). Repeat the experiment (Procedures #1-9). This time, however, a change in
the environment has led to no preference (random selection pressure) on your rabbit population. In
other words, the eagles eat brown and white rabbits equally. Remove 25% of the brown rabbits and
25% of the white rabbits in each generation. Calculate your new allele frequencies and plot them on
your graph.
Extra Credit Opportunity
On a separate sheet of GRAPH PAPER, draw a new G and g allele table and a new graph (just like the
ones in your lab report). Repeat the experiment (Procedures #1-9). This time, however, a change in
the environment has led to no preference (random selection pressure) on your rabbit population. In
other words, the eagles eat brown and white rabbits equally. Remove 25% of the brown rabbits and
25% of the white rabbits in each generation. Calculate your new allele frequencies and plot them on
your graph.
Extra Credit Opportunity
On a separate sheet of GRAPH PAPER, draw a new G and g allele table and a new graph (just like the
ones in your lab report). Repeat the experiment (Procedures #1-9). This time, however, a change in
the environment has led to no preference (random selection pressure) on your rabbit population. In
other words, the eagles eat brown and white rabbits equally. Remove 25% of the brown rabbits and
25% of the white rabbits in each generation. Calculate your new allele frequencies and plot them on
your graph.
Extra Credit Opportunity
On a separate sheet of GRAPH PAPER, draw a new G and g allele table and a new graph (just like the
ones in your lab report). Repeat the experiment (Procedures #1-9). This time, however, a change in
the environment has led to no preference (random selection pressure) on your rabbit population. In
other words, the eagles eat brown and white rabbits equally. Remove 25% of the brown rabbits and
25% of the white rabbits in each generation. Calculate your new allele frequencies and plot them on
your graph.
Name: ______________________________________________________ Date: ____________________________ Period: ___________
Natural Selection and Allele Frequency
Background:
___________________________________ can be described as the change in ________________________ frequencies of a
________________ ________________ over time. Natural selection can place pressure on specific
___________________________________ and cause a change in the frequency of ______________________ that produce
the phenotypes. In this activity, you will simulate the effects of ____________________ predation on a
population of rabbits, where _____ represents the homozygous dominant condition for brown fur,
_____ is the heterozygous condition for brown fur, and _____ represents the homozygous recessive
condition for white fur.
Procedure:
Make sure you correctly calculate allelic frequencies after each generation!
Allele G
Allele g
Generation
Number
Percentage
Frequency
Number
Percentage
Frequency
Start
50
50
0.50
50
50
0.50
1
2
3
4
5
Analyze & Conclude:
1. Did either allele disappear? Why or why not? _______________________________________________________________
______________________________________________________________________________________________________________________
______________________________________________________________________________________________________________________
______________________________________________________________________________________________________________________
2. What does your graph show about allelic frequencies and natural selection? ____________________________
______________________________________________________________________________________________________________________
______________________________________________________________________________________________________________________
______________________________________________________________________________________________________________________
3. What would happen to the allelic frequencies if the number of eagles declined? ________________________
______________________________________________________________________________________________________________________
______________________________________________________________________________________________________________________
______________________________________________________________________________________________________________________
4. Is this population of rabbits evolving? Why or why not? ___________________________________________________
______________________________________________________________________________________________________________________
______________________________________________________________________________________________________________________
______________________________________________________________________________________________________________________
Graph: Make sure to LABEL your axes and TITLE your graph.