Polygenic Traits: How multiple genes affect human height
Polygenic inheritance is a pattern whereby traits are controlled by
multiple genes.
This is different from the
simple mendelian
pattern because in
mendelian inheritance
a trait is controlled by only ONE gene, with
two possible versions. As a result there are only two possible
phenotypes: dominant or recessive. Even in
codominant
and
incomplete
dominance
inheritance patterns, only one gene controls the three possible phenotypes.
In this activity, you will use popsicle sticks to represent different chromosomes that each include a gene coding
for the height of an individual. In other words, the height trait will be controlled by multiple genes.
After tabulating all class data, you will make a bar graph to represent the resulting possible heights.
What you need to know before you start
• In this lab, height will be controlled by six genes (A, B, C, D, E and F).
• Each gene has two alleles, one dominant and one recessive: A/a, B/b, C/c, D/d, E/e, F/f
• The uppercase letter represents the dominant allele. The lowercase letter represents the recessive allele.
The genes are located on different chromosomes, so the inheritance of one allele does not affect the
inheritance of another (i.e. independent assortment).
• Tossing all six popsicle sticks represents the creation of a new zygote that has a particular combination
of alleles. Assume that the zygote has developed, the baby is born, and has grown to its adult height
when your record your data.
1. Obtain a collection of six popsicle sticks. They should all be different, labeled A/a, B/b, C/c, D/d, E/e,
and F/f.
2. The capital letters on one side represent a dominant allele for that particular gene. The
lower case
letters on the reverse represent the
recessive
allele.
3. Carefully toss all six popsicle sticks at once and allow them to land on the table. Read which letter
(capital or lower case) is facing up on each popsicle stick. In other words, you will ignore the letter that
is face down on the table.
4. Count the total number of dominant alleles facing up and the total number of recessive alleles facing
up. For example, you may see 2 capital letters and 4 lower case letters facing up. The result will be one
of the seven possible combinations shown in the “group data” row of your data table. Put a tally
mark in the box that corresponds to this combination.
5. Repeat steps #3-#4 for a total of 20 times. You should have a total of 20 tally marks in the “group
data” row.
6. Record your group data on the board. Once all groups have entered their data, the teacher will add
up the tallies in each column. Copy the totals in the “class data” row of your table. You will graph this.
