Polygenic Trait Lab Name _____________ Period ___

Purpose: This activity will demonstrate how polygenic traits work and why certain traits in a population are graphically represented by a bell curve, or "normal" distribution.

Procedure:

1) In this simulation, there are 3 genes (6 alleles) that control height. Each pair of students will flip 6 coins (3 by each "parent"). Each coin flip of heads will give an H₁ (the allele for tall) while tails gives an H₂ (the allele for short). A person's total height is a result of the cumulative effects of these 6 codominant alleles, as shown below:

2) Complete Table 1 below by recording the number of heads & tails that result from each set of 6 coin flips. Repeat this process 10 times, representing 10 different children.

3) Complete Table 2 below by summing the results from Table 1. Record your results from Table 2 on the board and calculate the class average when the data set is complete.

Results:

Table 1: Number of heads and tails flipped (out of 6) for each of your ten babies.

Table 2: Number of times you obtained each heads:tails combination (See Table 1).

Figure 1: Construct a frequency histogram from your Table 2 data. The number of occurances of H₁ and H₂ will go on the X-axis while the number of times that the situation occurred will go on the Y-axis. One set of bars will represent your totals and another set of bars will represent the class average in decimal form. Color them differently to distinguish between them. (See the example below)

Questions:

1) Each parent gives what percentage of their genetic material to their children? ____

2) If a male is 5 feet 9 inches tall, then he has 4 H₁ alleles and 2 H₂ alleles. He can only give 3 of his 6 alleles to his child. What are all the possible combinations?

3) If dad is 5 feet 7 inches tall and mom is 5 feet 5 inches, show why it is possible for them to give their child the necessary alleles to be 5 feet 11 inches tall. (Hint: start by filling in the baby's alleles)

4) If both parents are 5 feet 7 inches, it is possible for them to have a child that is more than 6 feet tall? Show which alleles each parent must give to make this possible:

5) If a man is 5 feet 5 inches tall and a woman is 5 feet 1 inches tall, what is the tallest height that their child could attain? _______ Show your work below:

6) If a man is 5 feet 7 inches tall and a woman is 5 feet 1 inches tall, what is the shortest height their child could attain? _______ Show your work below:

7) If height was controlled by a single gene, then the resulting phenotypes would be discrete (tall and short or perhaps tall, medium and short) and easily distinguished. A polygenic trait is one that is controlled by many genes. As a result, the range of phenotypes is continuous. In this case, there should be individuals of a variety of heights, from very short all the way to very tall. Is skin color polygenic? Explain:

8) Why do you think that the average height in the U.S. today is several inches more than it was about 100 years ago? (Hint: it has nothing to do with genetics)

9) On a separate piece of paper, make a frequency histogram of height for all of the students in your class.