Multifactorial Traits:

Genomics at the Cellular and Gene Level

Multifactorial traits are exactly like they sound, traits controlled by multiple factors, or in this case, traits controlled by multiple genes and the environment. Most of our traits fall into this category. They are traits that vary slightly from individual to individual, such as height and hair color as well as the common chronic conditions such as heart disease, diabetes, and cancer that we looked at in the activity What is Your Risk for Disease, with the Genomisons.

The following sequence of activities is designed to help your students continue their investigation into how characteristics of living things are passed on from generation to generation. This time we are looking at multifactorial traits and how the genes and environment play a role in the final expression of the trait. As you look through the activities you may decide to use just a few along with your current curriculum or you may decide to use them all. Just be sure to include enough experiences for your students so they can see a pattern behind the inheritance of multifactorial traits. This will help them apply these ideas later as they encounter new phenomena. This sequence also investigates a common topic in biology classes, the cell cycle. Here the students learn about the cell cycle in the context of cancer, a loss of cell cycle control. The cancer we focus on is skin cancer because we felt it was the most relevant one for high school students who are always searching for that perfect tan.

Activity Sequence

"Alike, But Not the Same," NIH Curriculum Supplement Series, Human Genetic Variation, activity 1.

This activity introduces the idea of multifactorial traits by allowing students to see that humans share many basic traits but that there is a wide range of variability in these human traits. This is because they are influenced by genetic and environmental factors. The students will collect data about certain human traits in their classroom, construct graphs from the data, and play a quick game showing how each of us is unique.

"Alike, But Not the Same" Michigan Benchmarks
AAAS Benchmarks 1B and 1A
National Science Content Standard A

To download the lesson plan and copy masters click here. It is Activity One in the module. The instructions for downloading are given at this site.

To view the entire module:Human Genetic Variation.


"Are You Susceptible," NIH Curriculum Supplement Series, Human Genetic Variation, activity 4.

In this activity, the students take a closer look at a multifactorial condition that was introduced as a problem for the Genomisons. The problem is heart disease. First, they look at how environmental factors, or the choices they make, play a role in determining the age of onset for this condition. Then they add in the genetic factors to see that in some cases the age of onset can change because of their genes. What surprises them is that genes play a part in heart disease and that genes can be helpful as well as detrimental. A model for how genes can play a part in multifactorial conditions is described in the activities to follow.

"Are You Susceptible" Michigan Benchmarks
AAAS Benchmarks 1B, 5B and 6E
National Science Content Standards F and G

To download the lesson plan and copy masters click here. It is Activity Four in the module. The instructions for downloading are given at this site.

To view the entire module:Human Genetic Variation.


The following two activities provide the students with a model for how genes play a part in multifactorial conditions

1) "Human Variation," DOE-Supported Curriculum from BSCS, Genes, Environment, and Human Behavior, activity 2.

This activity has the students use a 6 gene model along with environmental factors to explain the continuous variation for human height that was measured in the previous activity, "Alike, But Not the Same." Using the data they collect, they see that the multifactorial model is better than the single gene model when explaining the inheritance of height. It is nice to use a physical trait that can be measured, such as height, when you are first trying to understand how more than one gene can influence a single trait. Here they are adding or subtracting from the height depending on the alleles they receive from their parents for each of the 6 genes.

Michigan Family History Benchmarks
AAAS Benchmarks 1A, 1B and 5B
National Science Content Standards A and C

To download or order the entire module, Genes, Environment, and Human Behavior, click here. It is the second module in the list, and we are focusing on the second activity in that module. You may want to check out the others listed there, they are also valuable resources.

2) "Fingerprint Ridge Count: a polygenic trait useful in classroom instruction," by Mendenhall, Mertens, and Hendrix, American Biology Teacher, April, 1989.

This is a great activity to use with students as they learn how multiple genes can contribute to one phenotype. They collect their own fingerprints (which they love to do) and calculate their total ridge count (TRC). After comparing the data they collect from the class, they learn how to use a 4 gene model to predict the TRC for individuals in various problems. In this activity, the TRC depends on the alleles the individuals receive from their parents for each gene. One allele for each gene adds ridges and the other allele has no effect. Once the activity is finished, ask the students to predict their own genotype based on this model and their TRC. Understanding this model helps the students when they encounter more complicated examples of multifactorial traits.

Michigan Family History Benchmarks
AAAS Benchmarks 1A, 1B and 5B
National Science Content Standards A and C


"Cancer and the Cell Cycle," NIH Curriculum Supplement Series, Cell Biology and Cancer, Activity 2.

In this activity, the students investigate the biological cause of cancer, another multifactorial condition. They begin by using animations on a CD-ROM that helps them identify several seemingly unrelated causes of cancer. Again, using the CD-ROM, they investigate the groups of genes that control the cell cycle and what can happen if these genes are damaged. By putting two and two together, they come up with a hypothesis as to how each cause of cancer is related to the loss of cell cycle control and how they each cause cancer.

Michigan Cancer Benchmarks
AAAS Benchmarks 1A, 1B and 5B and 5C and 6E
National Science Content Standards A and C and E and G

To download the lesson plan and copy masters click here. It is Activity Two in the module. The instructions for downloading are given at this site.

To view the entire module, Cell Biology and Cancer, click here. If you have the time, I would recommend working through the entire module. It is a nice sequence of activities that take the inquiry approach for understanding how scientists are piecing together the mystery behind this multifactorial disease.

"Understanding Cancer," Cell Biology and Cancer, read this very interesting section of the module to increase your background knowledge.

More on Cancer as a Multifactorial Disorder, The Genetic Science Learning Center, the University of


Three Gene Cell Cycle/Cancer model

In this activity, the students will use their knowledge of the cell cycle and the genes that control it to predict whether or not several individuals, who have a certain combination of genes, will develop cancer. It gives the students an opportunity to use the knowledge they obtained from the previous activity, "Cancer and the Cell Cycle." Looking at the interaction of multiple genes is complex and the students will need to practice using their new knowledge.

Michigan Cancer Benchmarks
AAAS Benchmarks 1A, 1B and 5B and 5C and 6E
National Science Content Standards A and C and F and G


The following two activities have the students design experiments to investigate the effect of UV light on cells who have lost their DNA repair system.

1) "Experiments Designed by Students: UV Sensitive Yeast Experiment," by Lisa Weise and Veronica Vachon (Holt High School), MSTA Journal, Fall 2004.

To understand how skin cancer (or any other disease) is caused in humans, scientists will often use other organisms with genes similar to ours. These organisms usually grow faster and are easier to work with in the lab. For example, in this activity the students are working with a strain of yeast that lacks the DNA repair system that was investigated in the Three Gene Cell Cycle/Cancer Model Activity. If their DNA is damaged by UV light they will be unable to repair it and consequently they will not be able to grow as well as the wild type. This teacher had her students design their own investigations around the effect of UV light (an environmental factor) on this specific genetic strain of yeast.

Michigan UV Light Benchmarks
AAAS Benchmarks 1A and 1B and 5B and 5C
National Science Content Standard A and C

The yeast can be ordered from Carolina Biological as a kit.

2) "Evaluating Claims About Cancer," NIH Curriculum Supplement Series, Cell Biology and Cancer, activity 4.

As a parallel to the student designed experiments above, this activity also has students designing controlled experiments using UV sensitive yeast. First, the students identify claims that the media has made about sun exposure and skin cancer. Then, they design, carry out, and report the results of an experiment to test one of these claims. The students quickly learn that the UV sensitive yeast is a great organism for testing how well products protect us from skin cancer. The damage the UV light causes is detected quickly in the UV sensitive yeast, unlike a cell that has a functioning DNA repair system.

Michigan UV Light Benchmarks
AAAS Benchmarks 1A and 1B and 6E
National Science Content Standards A and F and G

To download the lesson plan and copy masters click here. It is Activity Four in the module. The instructions for downloading are given at this site.

To view the entire module, Cell Biology and Cancer, click here. If you have the time, I would recommend working through the entire module. It is a nice sequence of activities that take the inquiry approach for understanding how scientists are piecing together the mystery behind this multifactorial disease.


"Acting on Information About Cancer," NIH Curriculum Supplement Series, Cell Biology and Cancer, activity 5.

The link between UV light exposure and skin cancer suggests that skin cancer could be avoided if we reduced our sun exposure. In this activity, the students gather information on whether to support or oppose a proposal that requires everyone under the age of 18 to wear protective clothing when they are outside during the peak hours of the sun. Through the help of the CD-ROM (or the paper alternative), the students hear the opinion of 12 different people on this issue (many are quite humorous from the students perspective). Then they use the reference database to search for factual information related to this proposal. This activity presents the students with an interesting dilemma. Do they support the side that promotes healthy individuals and society or do they support the side that promotes freedom of choice?

"Acting on Information about Cancer" Michigan Benchmarks
AAAS Benchmarks 6E and 7D
National Science Content Standards F

To download the lesson plan, copy masters, and paper alternative to the CD-ROM click here. It is Activity Five in the module. The instructions for downloading are given at this site.

To view the entire module, Cell Biology and Cancer, click here.

For information on how to order UV Sensitive Beads, click here.


Now your students may ask:

"How does mutating a gene make it function differently or not at all?"

"Are all mutations for a single gene the same? Or can there be different mutations for the same gene?"

"If there are different mutations for a single gene, do they all have the same effect when it comes to gene expression?"

"How can scientists determine if an individual has a harmful combination of genes that could lead to a common chronic condition such as cancer, diabetes or heart disease?"

To answer these questions and more, we need to move to the molecular level. Look at the activities under Genetic Variation.