Pedigree Analysis

A pedigree is made to give an overview of the inheritance pattern and frequency of a (suspected) hereditary trait. Each family member is represented by a symbol: circle (female) or square (male), which is filled or black for affected individuals and empty or white for normal individuals. Mating is illustrated by a connecting horizontal mating line, their offspring is depicted beneath a vertical offspring line, and siblings are attached to a horizontal sibship line. Each generation is assigned a Roman numeral (I, II, III etc.) and each individual of a generation is assigned an Arabic numeral (1, 2, 3 etc.).

Common symbols used to build a pedigree tree: shape is used to represent an individual's sex. Males are depicted as squares and females depicted as circles. A diamond in used for individuals with undefined sex. Deceased individuals are represented by a diagonal slash through their symbol. Affected individuals are represented by a filled or shaded shape, rather than a blank or light shape. Carriers for a trait have their symbols half filled or shaded. The patient who is initiating a genetic work-up, or the proband, is indicated by an arrow pointing to a specific shape on the tree. Mating individuals have their shapes connected by a horizontal line.

Figure 1: Explanation for pedigree symbols

A proband is the individual who is the first affected family member who seeks medical attention regarding this phenotype (disease). Among the older generations from this family, there may have been other affected members; however, the proband typically refers to the member seeking medical attention or being studied, even if affected ancestors are known.