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Young: Medical Genetics

Pedigree Examples

Constructing a Family Tree

The construction of a family tree forms the basis of almost every genetics consultation. This is considered at length in Chapter 13 (pages 244-245), where guidance is given on how to draw up a family pedigree using information provided by relevant family members. Page 244 also includes details of the symbols commonly used for this purpose (Figure 13.1).

Three examples are provided below to illustrate the basic principles involved, and to demonstrate that a carefully constructed pedigree can sometimes yield information not only on the underlying pattern of inheritance but also on the specific underlying diagnosis. Example 1 reviews the recommended steps involved in taking a family history and drawing up the pedigree. In examples 2 and 3, details of the family history are provided and you are invited to use these to construct the family tree and then draw conclusions on the most probable underlying pattern of inheritance.