Hardy Weinberg Goldfish Lab

A delicious way to teach the Hardy Weinberg Principle

The Hardy-Weinberg equation can be used to determine whether or not a population is evolving.
Hardy-Weinberg Equation. Heather Scoville

One of the most confusing topics in Evolution for students is the Hardy Weinberg Principle. Many students learn best by using hands-on activities or labs. While it's not always easy to do activities based on evolution-related topics, there are ways to model population changes and predict using the Hardy Weinberg Equilibrium Equation. With the redesigned AP Biology curriculum stressing statistical analysis, this activity will help reinforce the advanced concepts.

The following lab is a delicious way to help your students understand the Hardy Weinberg Principle. Best of all, the materials are easily found at your local grocery store and will help keep costs down for your yearly budget! However, you may need to have a discussion with your class about lab safety and how normally they should be not eating any lab supplies. In fact, if you have a space that is not near lab benches that could be contaminated, you may want to consider using that as the work space to prevent any unintentional contamination of the food. This lab works really well at student desks or tables.

Materials (per person or lab group):

1 bag of mixed pretzel and cheddar Goldfish brand crackers

[Note: They make packages with pre-mixed pretzel and cheddar Goldfish crackers, but you can also buy large bags of just cheddar and just pretzel and then mix them into individual bags to create enough for all lab groups (or individuals for classes that are small in size.) Make sure your bags are not see-through to prevent unintentional "artificial selection" from occurring]

Remember the Hardy-Weinberg Principle: (A Population is at Genetic Equilibrium)

  1. No genes are undergoing mutations. There is no mutation of the alleles.
  2. The breeding population is large.
  3. The population is isolated from other populations of the species. No differential emigration or immigration occurs.
  4. All members survive and reproduce. There is no natural selection.
  1. Mating is random.


  1. Take a random population of 10 fish from the "ocean". The ocean is the bag of mixed gold and brown goldfish.
  2. Count the ten gold and brown fish and record the number of each in your chart. You can calculate frequencies later. Gold (cheddar goldfish) = recessive allele; brown (pretzel) = dominant allele
  3. Choose 3 gold goldfish from the 10 and eat them; if you do not have 3 gold fish, fill in the missing number by eating brown fish.
  4. Randomly, choose 3 fish from the “ocean” and add them to your group. (Add one fish for each one that died.) Do not use artificial selection by looking in the bag or purposefully selecting one type of fish over the other.
  5. Record the number of gold fish and brown fish.
  6. Again, eat 3 fish, all gold if possible.
  7. Add 3 fish, choosing them randomly from the ocean, one for each death.
  8. Count and record the colors of fish.
  9. Repeat steps 6, 7, and 8 two more times.
  10. Fill in the class results into a second chart like the one below.
  11. Calculate the allele and genotype frequencies from the data in the chart below.

Remember, p2 + 2pq + q2 = 1; p + q = 1

Suggested Analysis:

  1. Compare and contrast how the allele frequency of the recessive allele and dominant allele changed over the generations.
  1. Interpret your data tables to describe if evolution did occur. If so, between which generations was there the most change?
  2. Predict what would happen to both alleles if you extended your data to the 10th generation.
  3. If this part of the ocean was heavily fished and artificial selection came into play, how would that affect future generations?

Lab adapted from information received at the 2009 APTTI in Des Moines, Iowa from Dr. Jeff Smith.

Data Table

GenerationGold (f)Brown (F)q2qpp22pq