Establishing Hardy-Weinberg Equilibrium

Judith Jones

Teacher Instructions:

Purpose: The purpose of this activity is to help students understand how Hardy-Weinberg Equilibrium is established and what assumptions and conditions are necessary to reach Equilibrium.

Materials

(based on a class of 30)

• 60 cards with 'A' alleles (3 x 5 cards cut in half work well)
• 240 cards with 'a' alleles
• 25-30 students

Initial Preparation

The teacher should:

1. Prepare 60 cards with 'A' on each card.

2. Prepare 240 cards with 'a' on each card.

3. Optional: you could laminate the cards so that they last longer.

4. Place the cards upside down in a 'pool' to simulate the gene pool. You could use a small plastic children's swimming pool. You can also use a paper bag.
   
   IMPORTANT: Do not mix the 'A' and 'a' alleles thoroughly; just slightly overlap the two piles. You do not want your initial count to be in Hardy-Weinberg Equilibrium.

5. You will help students select 10 cards. Try to keep students from reaching all over the 'pool.'

6. You will be recording the class data on the board (see student instructions). Make sure that students record the class data in their charts. You could make a transparency of the student chart page and record class data using the overhead projector.

7. Initially, you may need to help students calculate frequencies.
   
   

   Stress to the students that Hardy-Weinberg Equilibrium is only achieved if:

   1. There is a large population;
      
      
   2. There is random mating.
      
      
   3. There is no selection for a particular allele.
      
      
   4. There are no mutations.
      
      
   5. There is no migration or isolation.
      
      

Establishing Hardy-Weinberg Equilibrium

Student Instructions:

Purpose

Procedure:

1. From the gene pool, select 10 cards, and then go back to your seat.

2. Count how many 'A' alleles you have and how many 'a' alleles you have.

3. After your teacher finishes adding up the total count for the class, record the class totals in your chart.

4. Calculate the frequencies of A and a in your class and record.

5. Now randomly pair your alleles so that you have 5 sets of alleles just like the genotypes of diploid organisms.

6. After your teacher counts the total AA, Aa, and aa combinations in the class, record these numbers in your chart.

7. Calculate the frequencies of each of these combinations in your class and record.

8. Spread your 10 cards out in one hand as if you were playing cards. Make sure that you are the only one who can see the alleles.Go around the room and find another person to trade with. Let that person take one of your alleles. You take one of their alleles. (Don't peek!) Now take your new allele and put it away so that you don't trade it again.

9. Trade 4 more alleles with 4 more people (only 1 trade with each person).

10. When you have only 5 alleles left in your hand and 5 new ones that are trades, sit down!

11. Again, pair up your 10 alleles randomly so that you have 5 pairs.

12. After your teacher counts the total AA, Aa, and aa combinations in the class, record these numbers in your chart.

13. Calculate the frequencies of each of these combinations and record.

14. Repeat steps 8-13 at least 1 more time or until your frequencies seem to be remaining stable.

CHART 1 (Class Totals)

	a	A	TOTAL
COUNT
FREQUENCY			1

	COUNTS				FREQUENCIES
	AA	Aa	aa	TOTAL	AA	Aa	aa	TOTAL
ROUND 1								1
ROUND 2								1
ROUND 3								1
ROUND 4								1

Once you have reached stability, calculate ideal Hardy-Weinberg frequencies using your frequency values for 'A' (p) and 'a' (q) and the Hardy-Weinberg equation: p² + 2pq + q²= 1

Class Values	Ideal Values
Final frequency for AA _____	Value of p2 _____
Final frequency for Aa _____	Value of 2pq _____
Final frequency for aa _____	Value of q2 _____

Analysis Questions:

1. What aspects of real populations did the following parts of the simulation represent?
   • the 'pool':
   • the paper cards:
   • tputting the paper cards in pairs:
   • texchanging cards with other people:

2. What initial assumptions did you make about your population in order for it to achieve Hardy-Weinberg Equilibrium?

3. How close were your final AA, Aa and aa frequencies to the ideal values?

4. What will happen in the next generations if the environment changes and the 'a' allele has a slight disadvantage? Answer in terms of frequencies.

5. Generally, how long does it take for allele frequencies to change significantly, if Hardy-Weinberg conditions are not met?

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