Family History:

Genomics at an Organism Level

As we help our students understand how characteristics of living things are passed from generation to generation we often use a family tree or pedigree to illustrate the movement of the characteristic through each generation. To be useful, the family tree or pedigree must become easy for the students to construct as they organize data involving characteristics in families. The data may involve single gene inheritance or the inheritance of multifactorial traits (multiple gene and environment interaction).

Activity Sequence

Step One: Understanding Pedigree (Family Tree) Design

Pedigree (Family Tree) Symbols and RelationshipsStudents must first become familiar with the symbols and how they are connected to form a pedigree. (For more information about the recommended universal pedigree symbols click here. They have symbols that reflect all of the new technology involved with reproduction.)

Modeling Pedigree Design: As the teacher, you can model how to use these symbols by constructing a pedigree. Begin with a simple family of four: mother, father, son and daughter. Then have the students suggest different relationships to make the family pedigree expand to four generations while trying to include all the possible relationships that can exist with the given symbols. (As another modeling activity, you may have them help you diagram the family trees for the characters in a popular soap opera or TV show)

Practicing Pedigree Design: Watching you sketch a pedigree is not enough of an experience for the students to master this skill. They will need to practice designing pedigrees for themselves. This is a time when they will need some support, so while working in groups have them do the Pedigree Swap.

Designing Pedigrees Solo: Eventually, each student must be able use the pedigree as a tool to describe the relationships within a family. Have them try the very famous "Ultimate Pedigree Challenge" with a twist. By the time they are finished with these, constructing pedigrees will be a breeze and they can focus more on the traits being followed through the family and how they are inherited. Your students will naturally want to design their own family tree. Here is a website to help them.

Step Two: Using the Pedigree as a Tool to Trace Characteristics from Generation to Generation

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

Now your students are ready to trace characteristics controlled by single genes from generation to generation using pedigrees. There are many modes of inheritance for single genes. As students practice assigning genotypes to individuals in a pedigree for a particular mode, they should notice a pattern that is true for that particular mode of inheritance and not true for others. Help them see the pattern in the first one and then see if they can identify the patterns in the ones that follow. Below are examples of pedigrees for different modes of inheritance for single gene traits. Included on each page is a list of the patterns students will discover for each mode of inheritance as well as areas of difficulty for students. Each of these pedigrees was designed to show the patterns for this mode of inheritance and may not be typical for rare single gene conditions. However, each page also has some real examples of human traits that we believe follow this mode of inheritance. Some will also have examples of more realistic pedigrees for specific conditions. Remember, when assigning genotypes to pedigrees always begin with the individuals who have only one possible genotype and work from there by looking at their relationship to the other members of the family.

As the students get better at doing this, try giving them a pedigree exhibiting a new mode of inheritance without telling them what it is and see if they can hypothesize what the possible mode could be. This will be a challenge, but it allows them to use their understanding of how genes move from generation to generation in a different way. You may decide to study only a couple of modes of inheritance or you may have the time to do them all as you look at different conditions throughout your genetics unit or class. These are designed to support what you already have developed.

Autosomal Recessive
Autosomal Dominant
Sex(X)-linked Recessive
Sex(X)-linked Dominant
Sex Influenced female dominant
Sex Influenced male dominant
Y-linked
Sex Limited
Mitochondrial

Now that they are familiar with the different modes of inheritance and their patterns of genotypes, they can use their knowledge to analyze pedigrees to identify possible modes of inheritance for a specific condition. Here are two examples. If they can analyze these they can analyze anything!

Three Separate Families, One Genetic Condition
The Super Pedigree Analysis

Step Three: Using the Pedigree as a Tool to Collect a Family History of Common Chronic Disorders

Michigan Family History Benchmarks
AAAS Benchmarks 5B, 1A, 6E
National Standards A and C and F

Unlike single gene disorders that are very rare, common chronic disorders such as heart disease, cancer, and diabetes will sometime, directly or indirectly, impact all of our lives. These conditions have been found to run in families. Scientists now know that the appearance of these disorders is influenced by our genetics, environment, and behavior. We can't change our genes but we can impact their expression. "Genes draw your road map, but you still chart your course.....and a genetic predisposition is just that: it is not destiny but rather a tendency that can be encouraged or discouraged to express itself by how we live our lives." (Jane E. Brody, NY Times, February 25, 2002)

Collecting your family history for these common chronic disorders is the first step toward prevention. Help your students to see how this is done as they use their knowledge of pedigrees and gene transmission to work through the activity, "What is Your Risk for Disease?". Here they will meet the Genomisons and help them calculate their risk for several common chronic conditions.

Your students will notice that trying to assign genotypes for the chronic disorders found in the Genomisons activity is not so easy. That is because these common chronic conditions are not controlled by single genes but are multifactorial. Your students may begin gathering information about their family history by completing a Health Family Tree at this website.