Judith Jones and Judith Stanhope
1994 Woodrow Wilson Biology Institute
One of the five conditions that must be met
if a population is to maintain Hardy-Weinberg Equilibrium is no
natural selection. The purpose of this activity is to demonstrate
that natural selection is an agent of evolution (the change in
gene frequencies over time). Students quantitatively apply the
Hardy-Weinberg Principle to an imaginary population of fish.
Target Age/Ability Group
High School / 10th grade Biology. Students need to be familiar
with HardyñWeinberg Equilibrium.
One class period of 60 minutes
Math and graphing skills, collecting and analyzing data, cooperative
and collaborative learning and critical thinking
Materials - For class of 30
- goldfish bowl or other large bowl
- 1 8 1/4 oz. package of pretzel goldfish (called brown fish in the lab instructions)
- 8 1/4 oz. package of cheese goldfish (called gold fish in the lab instructions)*
- paper plates or towels to put fish on
*Note: You may choose to use other types of 'goodies'
such as chocolate and vanilla goldfish, Teddy Graham Bears (come
in four flavors), two different kinds of beans, or M & M's.
- Students must thoroughly wash their hands before starting the activity.
- Use paper plates on which the fish can be placed.
- Have students work in pairs. Each pair will do at least five
trials (generations). You may need to do more than five generations
to achieve or approach equilibrium.
- Supply paper plates for each student. This will enable students
to collect and remove fish in a clean fashion.
- Pour the brown (pretzel) and gold (cheese) fish into a large
pool (bowl). Mix thoroughly with a clean spatula.
- For logistical reasons, it may be best to place the fish bowl
in the center of the room. Students will be getting up and down
to randomly replace the fish eaten.
- Review with the students that they can assume the following:
- Birth rate equals death rate.
- Mating is random.
- There are no mutations.
- There are only two alleles in the population. Brown
(B) color is the dominant trait and gold (b) is
the recessive trait.
- The population should be large.
- Demonstrate to the students the procedure for eating the 3
gold fish and randomly replacing the eaten fish. Remember, if
there are not enough gold fish to eat, the students need to eat
the difference in brown fish.
- The data /results tables are shown in the student instructions.
- Draw on the board a class data sheet in which the students
will record their individual results. An example of what the class
totals may look like is shown below.
| Class Data - Totals
|Generation|| Brown Fish||Gold Fish|
- After students copy down the class totals, they will determine
the allele and genotypic frequencies for both the individual and
class data. Next, they will graph the individual and class allele
- In comparing the individual with class results, one should
see that the individual results do not approach Hardy-Weinberg
Equilibrium. The class results (a larger population) approach
- The graphs should show an increase in the frequency of the
brown colored allele and a decrease in the frequency of the gold
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