Figure 1. A pedigree showing a phenotype that is passed on over three generations.

Pedigree is a diagram used to show the phenotype of a particular gene documented over several generations. It is particularly useful to determine whether a phenotype is inherited or not and the method of inheritance (for example, dominant, recessive, sex-linked, or even penetrance).

A lot of information can be gathered by studying a pedigree. These symbols have specific meanings:

Figure 2. Explanation for pedigree symbols.

An individual that has deceased, shown with a diagonal line over the symbol, may be due to the phenotype or other reasons, for example, aging, accidents, or other phenotype (other unrelated disease).

One can also add information regarding the phenotype or other phenotypes that may be related. For example, one can mention breast cancer under the affected symbol accompanied with the age of diagnosis. An individual can suffer from several related phenotypes, for example, both breast cancer and ovarian cancer because these two phenotypes have been previously determined to be related to the same genes (e.g., BRCA1 and BRCA2).

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.

Mendelian inheritance


Theory overview