DNA photo
  Children's Hospital Research  Children's Hospital Labs
Engle Laboratory  Children's logo  Harvard logo
 Engle Lab Home Page
 X  X
How to draw your pedigree
> Linkage analysis
A pedigree, or drawing of a family tree, is a pictorial representation of a family. The construction of an accurate family pedigree is fundamental to the provision of clinical genetics services and serves as an informational framework for human genetic research. Its great strength is that it allows a lot of clinical and family information to be seen at a glance.

The symbols and rules to construct a pedigree using standardized human pedigree nomenclature can be found in the American Journal of Human Genetics 56:745-752 (1995). The following tutorial describes only basic symbols and rules. For complex family situations, please refer to the above journal article and/or visit the American Society for Human Genetics family history url: http://www.ashg.org/genetics/ashg/educ/007.shtml

The basics

As shown below, males are depicted as squares, females as circles, and individuals of unknown sex as diamonds. A union (previously used to show a marriage, but now shows a broader spectrum of relationships) is shown by connecting two individuals with a solid horizontal line. This line is called the "relationship" line. Usually the male is drawn to the left of his female partner. If the union is between individuals that are related to each other (have a common ancestor) the relationship line is a doublet. If the union produces any children or pregnancies, a vertical line is drawn from the relationship line. This vertical line is called the "line of descent". The line of descent may connect to a horizontal "sibship" line. "Individual" lines from the sibship line are drawn to an individual's symbol to show a child of the union.
Image
Special symbols

Pregnancies are drawn as triangles, or diamonds with a capital 'P' in the center (if the sex of the pregnancy is known, a square or circle with a 'P' can be used). Twins (or triplets) are drawn like cherries off of the sibship line. Individuals who have passed away have a diagonal line drawn through their symbols. An individual's symbol may be shaded or hatched to show particular clinical status, which is interpreted in a legend or key. It is not uncommon to see notations next to an individual's symbol. These notations may state the individual's date of birth or other information of interest.

Below is an example of a family showing parents with their 4 children (2 girls and twin boys). The mother is pregnant (unknown sex) at 20 weeks gestation. The father had a brother (now deceased). The mother has a sister and a brother. The sister has one son. The father, his mother, his deceased brother, and one of his daughters have/had congenital ptosis. Notice that each generation can be found in the same horizontal field, horizontal lines only connect individuals involved in a union, and that siblings are connected through vertical lines attached to a common horizontal "sibling" line.

Image
 X  X