Polygenic traits with pennies

Uses the results of flipping pennies to represent the functioning of polygenic traits.

A lesson plan for grades 9–12 Science

By Buie Sadie, James Caldwell, Jeanette Fredericks, Janice Shue, Katie Wadsworth, and Tracy Watson

About the authors

I teach AP Biology and Honors Biology II at Chapel Hill High School.

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Learning outcomes

Students will understand polygenic traits, how they work, and how parents determine the polygenic trait of a child.

Polygenic traits or quantitative genetics is a topic that is often skipped by biology teachers. It seems that teachers have no real model or lab in which to demonstrate this complicated topic. We have found that if we use pennies to represent genes (heads are dominant or active alleles, tails are recessive or inactive alleles), we could show students how people fall into a bell curve arrangement and how different heights (or other traits) are passed on to children.

Polygenic traits are traits that are controlled by more than one gene, i.e. height, weight, hair color, skin color (basically, anything that deals with size, shape and color). This allows for a wide range of physical traits. For example, if height was controlled by one gene A and if AA= 6 feet and Aa = 5 feet 7 inches and aa= 5 feet, then people would be one of three different heights. Since height is controlled by more than one gene, a wide range of heights is possible.

Once the pennies have been handed out (six for each group) and the procedures have been reviewed, the teacher will put a class result table on the board, so that the class can collect the data. Each group will record the number of times the following situations occured when the pennies were flipped.

• 0 Tails and 6 Heads
• 1 Tail and 5 Heads
• 2 Tails and 4 Heads
• 3 Tails and 3 Heads
• 4 Tails and 2 Heads
• 5 Tails and 1 Head
• 6 Tails and 0 Heads

Teacher planning

Time required for lesson

1 class period

Materials/resources

One Answer sheet

Per group:

• six pennies which will represent the genes for height

Per student:

• tables
• questions
• graph paper
• ruler

Pre-activities

Students should understand simple Mendelian genetics.

Activities

1. Each group will carefully flip all six coins on the lab table.
2. Record the number of heads and tails that result from the flip in table 1.
3. Continue to flip the six coins and continue to record the number of heads and tails that result from the flip until table 1 is complete.
4. Complete table 2 by adding up the number of times the following situations occurred.
   • 0 Tails and 6 Heads
   • 1 Tail and 5 Heads
   • 2 Tails and 4 Heads
   • 3 Tails and 3 Heads
   • 4 Tails and 2 Heads
   • 5 Tails and 1 Head
   • 6 Tails and 0 Heads
5. Record your results from table 2 on the board with the class results.
6. Record the class results in table 2.
7. Construct a bar graph from the class data. The number of heads and tails will go on the X axis (the independent variable), while the number of times the situation occurred will go on the Y axis (the dependent variable).
8. Answer the questions.

Assessment

• 5 points for table 1
• 5 points for table 2
• 10 points for the graph
• 20 points for the questions