Pedigree Analysis

One way scientists study the inheritance of traits and genetic disorders in humans is through the analysis of family trees, also known as pedigrees.

In a typical pedigree, squares represent males, circles represent females, and a horizontal line between these shapes represents a mating.

If such a union produces children, a vertical line is drawn downward from the parents toward the sons and daughters.

Progressively lower rows in the pedigree represent successive generations in a family.

Shaded symbols represent individuals affected by the trait or disorder. Half-shaded symbols represent carriers of a recessive disorder who are typically unaffected but can pass the mutation to offspring. A diagonal slash through a symbol indicates that the individual is deceased.

For example, in a pedigree for biotinidase deficiency, shaded symbols represent individuals diagnosed with the disorder, including those showing symptoms such as skin rashes.

Biotinidase deficiency results from absent or reduced biotinidase enzyme activity, which is responsible for recycling biotin or vitamin B7.

By assessing which family members have been diagnosed with biotinidase deficiency, researchers can determine whether this disease results from a recessive or dominant mutation in a single gene located on an autosome or a sex chromosome.

Here, males and females are affected at similar rates.

Unaffected parents can have children with the disorder, and not every generation contains a family member with the disease. This pattern suggests that biotinidase deficiency is autosomal recessive.

Importantly, pedigree analysis not only shows inheritance patterns but can also help couples understand their risk of having a child with the disorder, based on their family history.