Fishy Frequencies

Judith Jones and Judith Stanhope
1994 Woodrow Wilson Biology Institute

Teacher Guide

Introduction:

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.

Class Time

One class period of 60 minutes

Critical Skills

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.

Safety Precautions

Students must thoroughly wash their hands before starting the activity.
Use paper plates on which the fish can be placed.

Teacher Notes

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
1	79	73
2	95	57
3	112	40
4	120	32
5	129	23

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 frequencies.
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 equilibrium.
The graphs should show an increase in the frequency of the brown colored allele and a decrease in the frequency of the gold colored allele.

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