Pedigree Charts

Pedigree charts are used to track a trait through multiple generations in a family. They can also be used to predict the presence (or absence) of the trait in future generations.

Most pedigree charts use the same symbols to represent family members. Males are shown as squares and females are shown as circles. Individuals who have the trait being studied have their shape shaded in. Some pedigree charts show carriers of the trait as half-shaded shapes.

Showing Inheritance on a Pedigree Chart

You can use the information on a pedigree chart to determine if the trait being studied is autosomal dominant, autosomal recessive, or sex-linked.

Autosomal Dominant Traits

A pedigree chart showing the inheritance of an autosomal dominant trait.

The pedigree chart above shows an autosomal dominant trait. This chart has the genotypes under each shape, but this is not common. If presented with a pedigree without the genotypes listed, you can still determine the inheritance pattern of the trait. A trait that is dominant can result in two affected parents having unaffected children. This indicates that the parents were heterozygous (Aa × Aa) and the unaffected child inherited both recessive alleles (aa).

Autosomal Recessive Traits

A pedigree chart showing the inheritance of an autosomal recessive trait.

The pedigree chart above shows an autosomal recessive trait. A trait that is recessive can result in two unaffected parents having affected children. This indicates that the parents were heterozygous (Aa × Aa) and the affected child inherited both recessive alleles (aa).

X-Linked Traits

The inheritance of traits found on the X chromosome are harder to determine from pedigree charts than autosomal traits are. However, it is still possible to suggest that a trait may be X-linked based on the pattern of inheritance.

This trait may be X-linked and recessive.

The pedigree chart above suggests that this trait is X-linked and recessive. Generation III shows the offspring of a heterozygous female and an unaffected male. Two of the sons are affected, but none of the daughters are affected. This may be due to the sons inheriting their mother’s affected X chromosome.

This trait may be X-linked and dominant.

The pedigree chart above suggests that this trait is X-linked and dominant. The affected male in Generation I has all affected daughters but no affected sons. The daughters must have inherited one affected X chromosome from their father and one unaffected X chromosome from their mother. The son only inherited his mother’s unaffected X chromosome.

Page 1
Page 2
Page 3
Return to Lab Main Page
Print this page