Pedigrees

Isaac, Rebecca, Becca

Pedigrees and How to Understand Them

There are a few different reasons to make a pedigree. One reason is to just show how many offspring two individuals had, how many offspring they had, and what their sexes were. However, the main reason is to show how a trait is passed down from generation to generation. Did you get your unattached earlobe from your mom or dad? Who did they get it from? Making a pedigree is one way to trace the pattern of inheritance of a trait. It can be any trait that is not influenced by multiple alleles or polygenic inheritance. These simple traits and genetics are what we commonly refer to as “Mendelian Genetics.” The most important reason to make a pedigree is so that you can trace a disease and its likeliness of occurring throughout a family.

Symbols are very important when it comes to overall understanding of a pedigree and how it works. Simply put, if you do not understand the symbols, you will not understand the pedigree. Some symbols are more frequent then others, such as mating lines. Others are less common, such as the symbol for triplets. Your level of understanding, however, needs to be based upon which symbols affect your family. If you have three sets of twins in your family, you will need to know the symbol for twins well. If you have no twins in your family, you are less likely to need to know what it means. Also, when reading a pedigree, you need to be able to identify the symbols used within it. Listed below are the more common symbols of pedigree-making and their meanings.

There are different ways to pass on traits to offspring including simple Mendelian genetics, multiple allelic inheritance, polygenic inheritance, and sex-linked inheritance. So, in order to truly understand many of the inheritance patterns, pedigrees help organize the information to make it easier to read and quicker to understand. Mendelian genetics include simple dominant and recessive traits, like the ability to roll your tongue, attached earlobes, and a widow’s peak (picture underneath paragraph). Each parent has two alleles that they received from their parents, (one from each) and will pass on one to each of their offspring giving each child two alleles to be represented or masked. Multiple allelic inheritances are very similar to Mendelian genetics. Each offspring receives two alleles to be expressed. There are just more possibilities because there are more than two kinds of alleles for one trait. Blood type is a great example of this, because there are three kinds of alleles: A, B, and O. However, there are six combinations that a child could have: AA, AO, AB, BB, BO, and OO. Polygenic inheritance traits are traits that seem to have limitless possibilities such as skin color, height, and hair color. A human’s height, for instance, is made of the height of each body part, each which has many genes that control it. There are not any true dominant and recessive alleles, because the dominant alleles don’t truly mask the recessive. You can think of it simply as dominant alleles and recessive alleles “blending” together. So, the more dominant traits an offspring receives, (capital letters) the more the dominant traits will show. The chart below is for potential skin colors between two parents, both being AaBbCc. The more capital letters, the darker the skin color is.


 * **Gametes ** ||  **ABC **  ||  **ABc **  ||  **AbC **  ||  **Abc **  ||  **aBC **  ||  **aBc **  ||  **abC **  ||  **abc **  ||
 * **ABC ** ||  **6 **  ||  **5 **  ||  **5 **  ||  **4 **  ||  **5 **  ||  **4 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">4 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">3 **  ||
 * **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">ABc ** ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">5 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">4 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">4 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">3 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">4 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">3 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">3 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">2 **  ||
 * **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">AbC ** ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">5 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">4 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">4 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">3 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">4 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">3 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">3 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">2 **  ||
 * **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">Abc ** ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">4 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">3 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">3 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">2 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">3 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">2 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">2 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">1 **  ||
 * **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">aBC ** ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">5 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">4 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">4 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">3 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">4 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">3 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">3 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">2 **  ||
 * **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">aBc ** ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">4 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">3 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">3 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">2 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">3 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">2 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">2 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">1 **  ||
 * **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">abC ** ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">4 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">3 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">3 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">2 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">3 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">2 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">2 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">1 **  ||
 * **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">abc ** ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">3 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">2 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">2 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">1 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">2 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">1 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">1 **  ||  **<span style="font-family: 'Times New Roman','serif'; font-size: 13.5pt;">0 **  ||

Sex-linked inheritance, deals with sex chromosomes, which are passed from the mother and the father determining the sex of the offspring. Females have XX chromosomes, and males have XY. The disease or disorder is determined on either chromosome when it is a sex-linked trait. Y-linked disorders are never evident in women, because women do not receive a Y chromosome and therefore do not even have the possibility. Sex-linked traits can be either recessive or dominant depending on the disease.

Our Widget- This link leads to a site with an interactive way to test your knowledge of the use of pedigrees- []

A pedigree can be a good way to keep track of diseases in a family; affected carriers, ones with the disease, and those who don’t have any trace of it. An important reason to make a pedigree is to assess the risk that your children could inherit a genetic disease from either you or your partner. If the disease is something that could seriously affect the child’s life, assessing the risk can be very important. If it is serious, and your risk is high, you may decide to not even have children or to adopt. For example, a female carrier of hemophilia has a fifty percent chance of passing the disease on to her male offspring. The carrier gene has a fifty percent chance of passing between mother and daughter as well. Often, in these instances, it is best to not have any children. By doing this, you avoid passing on the gene. Hemophilia, as shown above, is one of the most common bleeding disorders. The blood does not clot as fast as it should, thus resulting in possible heavy bleeding from even the slightest wounds or scratches. When the bleeding is internal it can lead to organ and tissue damage. In any situation, it can be fatal due to the extreme loss of blood. Any bleeding cut can send you to the emergency room. Because of these reasons, persons with hemophilia tend to not have very long life spans. Most commonly, males are affected, as hemophilia is found in the X chromosome. Since females have two X chromosomes it’s more likely that at least one of their chromosomes will not be affected, thus masking the trait.

For more information: This site helps show how to create your own family pedigree and why it is nice to use pedigrees instead of other resources.-[] This site also gives you different traits, and helps you better understand how to form and create amazing pedigrees- []

Tyler Decker- More information on understanding pedigrees: [] Tyler Decker- More information on Hemophilia: []

Works Cited: [] [] [] [] [] [] [] [] ( Annika) -- this webside shows how to analyse a pedigree and talks about the different modes of inheritance. this side describe autosomal dominant, autosomal recessive, x-linked recessive and analyse the application of a pedigree.