Natural Selection: Fishy Frequencies
Adapted from: http://www.accessexcellence.org/AE/AEPC/WWC/1994/fishy.php
NC Essential Standard L.4.2/ Common Core: W2
Explain the relationship between genetic variation and an organism’s ability to adapt to its environment.
Introduction: There is a ton of genetic variation within almost
all species. Think about it—no two individuals have the same
DNA sequences unless they are identical twins! This genetic
variation contributes to phenotypic variation, which means the
physical appearance of individuals will be different! In this lab,
you will look at how genetics causes a species of fish to be two
different colors (gold and brown). When sharks infest the water
and start to favor one color of fish, what will happen to the fish
over time?
Objective: Observe and analyze the process of natural selection and role of genetic variation in
evolution.
Background Information: Before completing this lab, there are several facts you need to know
about the fish:
1. These little fish are the natural prey of the terrible fish-eating sharks- YOU!
2. The fish come with two phenotypes –gold and brown- depending on their genotype:


Gold: this is a recessive trait (ff)
Brown: this is a dominant trait (FF or Ff)
3. In the first simulation, you (the shark) will randomly eat whatever color fish you come in
contact with first. There will be NO selection.
4. In the second simulation, you prefer to eat the gold fish because they easier to see and easier
to catch. The brown fish taste salty and are sneaky and hard to catch. Therefore you will
ONLY eat gold fish unless none are available in which case you will be forced to eat the brown
fish to stay alive.
5. New fish are born every “year” and the birth rate equals the death rate. You will simulate
births by reaching into the pool of “spare fish” and randomly selecting fish.
Materials:
-Bowl (the “ocean”)
-pretzel goldfish (brown fish)
-cheddar goldfish (gold fish)
-paper plates
Procedure:
Simulation 1- No Selection
1. Close your eyes and randomly select a population of 10 fish from the “ocean” and put them on
your plate.
2. Count the number of gold and brown fish and record in your chart; you can calculate
percentages later.
3. Without looking at the plate of fish, randomly choose 3 fish to eat.
4. Again, without looking, choose 3 fish from the “ocean.” (One fish for each one that died.) Be
random. Do NOT use artificial selection.
5. Count and record the number of gold and brown fish on your plate.
6. Again, without looking, eat 3 fish, randomly chosen.
7. Again, without looking, add 3 randomly selected fish from the “ocean.”
8. Count and record the number of gold and brown fish on your plate.
9. Repeat steps 6, 7, and 8 two more times. Be sure that you are NOT looking while making
your selections.
10. Provide your results for the class. Fill in the class results on your chart.
Simulation 2- With Selection
1. Close your eyes and randomly select a population of 10 fish from the “ocean” and put them on
your plate.
2. Count the number of gold and brown fish and record in your chart; you can calculate
percentages later.
3. Eat 3 gold fish; if you do not have 3 gold fish, fill in the missing number by eating brown fish.
4. Without looking, choose 3 fish from the “ocean.” (One fish for each one that died.) Be
random. Do NOT use artificial selection.
5. Count and record the number of gold and brown fish on your plate.
6. Again eat 3 fish, all gold if possible.
7. Again, without looking, add 3 randomly selected fish from the “ocean.”
8. Count and record.
9. Repeat steps 6, 7, and 8 two more times.
10. Provide your results for the class. Fill in the class results on your chart.
Hypothesis: Do you think the percentage of gold and brown fish will change overtime during the
first simulation? If yes, how will it change? Why?
Do you think the percentage of gold and brown fish will change overtime during the second
simulation? If yes, how will it change? Why?
Data:
Simulation 1- Without Selection
Individual Data
Generation
Gold
Class Data
Brown
% Gold
%
Brown
Generation
1
1
2
2
3
3
4
4
5
5
Gold
Brown
% Gold
%
Brown
Gold
Brown
% Gold
%
Brown
Simulation 2- With Selection
Individual Data
Generation
Gold
Class Data
Brown
% Gold
%
Brown
Generation
1
1
2
2
3
3
4
4
5
5
Analysis:
1. Prepare a graph for Without Selection using the set of class data. On the “x” axis put
generations 1-5 and on the “y” axis put percentage (0-100). Plot both the gold and brown
class percentages and label the lines clearly (gold and brown). Include labels and a title.
2. Prepare a graph for With Selection using the set of class data. On the “x” axis put generations
1-5 and on the “y” axis put percentage (0-100). Plot both the gold and brown class
percentages and label the lines clearly (gold and brown). Include labels and a title.
3. In either simulation, did your percentages stay approximately the same over time? If yes,
which simulation?
4. Was your data different from the class data? How? Why is it important to collect class data?
5. With selection, what happens to the percentages from generation 1 to generation 5?
6. What process is occurring when there is a change in allele frequencies (percentages) over a
long period of time?
7. In simulation 2, what happened to the gold fish over successive generations and why?
8. In simulation 2, why don’t the gold fish entirely disappear from the population (Hint: Think
about the brown fish and their alleles!)
9. If the sharks continue to prefer to eat gold fish, what will eventually happen?
10. In what ways did these simulations represent real life? How were the simulations different
from real life situations?
Conclusion:
1. What genetic variation was seen in the fish population? How did this variation affect the way
the fish looked?
2. How did this genetic variation affect the fish’s ability to adapt to their environment? Which
color fish were better fit for this environment?
3. Explain how this simulation models the genetic variation and the processes of natural selection
and evolution.