Notes: Introduction to Pedigrees 1/27

A pedigree is a chart that shows the genetic relationship of family members and theirphenotypes. A pedigree can be used to determine the inheritance of a genetic trait, especially genetic diseases, across several generations of a family.

Symbols and pictures are used to construct pedigrees.

  1. A Male is represented

with the shape ______

  1. A Female is represented

with the shape ______

  1. A couple that is having children is represented with ______
  1. An individual in the family that has the trait (if it’s a disease we say they are “affected”) is represented with the shape ______.
  1. If the trait is recessive, a heterozygous individual is called a “carrier” and is represented with the shape ______.

The lines connecting two individuals indicate that they are married or mating to produce children. The vertical line shows that the individuals below it are the children of the married/mating pair. Each generation is shown in order, with the top individuals being the first generation, indicated with a roman numeral “I”.

Children are drawn and numbered in order of birth.

A pedigree can be used to help show the probability for two parents to produce offspring with a specific trait. Genetic counselorsare people who commonly use pedigrees to help couples determine if the parents will be able to produce healthy children.

Autosomal means the gene for the trait is found on any of the chromosomes EXCEPT the sex chromosomes (X and Y chromosomes determine the sex of the offspring). Therefore the individual’s sex does not determine the probability of having the trait.

Autosomal dominant traits have pedigrees that show the affected individuals, which could be either homozygous dominant or heterozygous. If the individual has at least one dominant allele, the trait will be expressed and the individual will be affected.

*Examples of Autosomal Dominant Genetic Diseases:

*Achondroplasia

*Huntington’s Disease

In the Pedigree for Huntington’s Disease on the right, notice the affected individuals are all heterozygous.

Autosomal recessive traits have pedigrees that show the carriers, which are heterozygous and are NOT affected. The affected individuals are all homozygous recessive, because there must be two recessive alleles for the trait to be seen.

Examples of Autosomal Recessive Genetic Diseases:

*Albinism*Cystic fibrosis

*Galactosemia*Tay Sachs Disease

In the Pedigree for Tay Sachs Disease on the right, notice the carriers are shown, and the affected individuals are homozygous recessive.