Pedigree Studies (Leaving Cert Biology): Revision Notes

Pedigree Studies

• Pedigree studies can be used to explain the inheritance of certain characteristics.
• Squares and circles are used to represent males and females.

This image is a pedigree chart showing how a genetic disorder is inherited through a family.

• Squares = males and circles = females.
• Red shapes = affected individuals (males fully shaded red, females fully shaded red).
• Half-red circles = carrier females, who carry one copy of the affected gene but do not show the disorder.
• Blue shapes = unaffected (normal) individuals.

From the pattern, the disorder is likely X-linked recessive, because:

• More males are affected than females.
• Females can be carriers without being affected.
• Affected males do not pass the disorder to their sons, but all their daughters become carriers.

In summary: the chart shows an X-linked recessive inheritance pattern, where the gene is passed through carrier females and expressed in affected males.