Understanding Your Family’s Pedigree

A pedigree is a genetic representation of a family tree that diagrams the inheritance of a trait or disease through several generations.  The pedigree shows the relationships between family members and indicates which individuals express or silently carry the trait in question.

Illustration of Autosomal Dominant Pedigree

This pedigree shows an autosomal dominant trait or disorder.  Autosomal means the gene is on a chromosome that is not a sex chromosome (X or Y).  Not all of the offspring inherited the trait because their parents were heterozygous and passed on two recessive genes to those that do not show the trait.  None of the offspring of two recessive individuals have the trait.  Examples of autosomal dominant disorders are Huntington’s Disease and Marfan Syndrome.

Illustration of Autosomal Recessive Pedigree

This pedigree is of an autosomal recessive trait or disorder.  The completely orange square represents a male that is homozygous recessive and has the trait.  All of the half-shaded individuals are carriers; they do not exhibit the trait because it is recessive, but they could pass it on to their offspring if their partner is also a heterozygote.  Autosomal recessive disorders include Cystic Fibrosis and Tay-Sachs Disease.

Source:   Biologydictionary.net Editors. “Pedigree”