Interpreting A Pedigree 

Many health care professionals have their own way of drawing a pedigree and may use slightly different symbols from time to time. However, the table below can serve as a guide in using and interpreting the most basic and commonly used symbols when drawing or reading a pedigree.

* A carrier is an individual who does not show any signs or symptoms of a genetic condition, but has the ability to pass on a disease-causing mutation to offspring.

A vertical line connects parent(s) to their children. Horizontal lines between individuals represent marriage or union. Horizontal lines connecting vertical lines represents that all connected individuals are siblings. For example, in the pedigree seen below, we see two couples represented at the very top of the diagram: one on the left and one on the right.

Click here for a larger version of this Pedigree

John James is married to Mary White James, and they have five children: Kathryn, John, Jr., Michael, Sarah, and Jack. William Black is married to Karen Smith Black, and they have three children: Jane, Sandra, and George. Jack James married Jane Black, and they had two children: Zachary and Melissa.

There are other things to be observed about this pedigree. For instance, five members of the James family have a genetic condition known as neurofibromatosis: John, Michael, Sarah, Anne, Dina, and John. This is indicated by the shapes being filled in with the color blue. We can see that John was diagnosed with neurofibromatosis at age 27, but there are no ages of diagnosis listed for the others. John James is deceased; according to this pedigree, he died in 1982 of respiratory failure. We can also see that John, Jr. has asthma, William Black had a heart attack when he was 62 years old, and Karen Smith Black has osteoporosis. The James family is of German and English descent, and the Black family is of Western European descent. Finally, the arrow by Melissa's name indicates that she is the member of this large, extended family who is currently seeking a consultation with a genetics professional. All of this information is available in this one drawing.   

A careful observer may have noticed that some mothers or fathers appear to be absent from this pedigree. For instance, we know that Kathryn is David's mother, but there is no information about his father! This is not necessarily because we do not know anything about David's father. Very often, a genetics professional drawing a pedigree will leave spouses or partners off in order to save room and to keep the drawing from getting too messy and complicated. This is okay, as long as this does not leave off any information that may be helpful in a case.