Pedigree Notes

What is a pedigree? A pedigree is a diagram of family relationships that uses symbols to represent people and lines to represent genetic relationships. Pedigrees are often used to determine the mode of inheritance (dominant, recessive, etc.) of traits and genetic diseases.

Rules for Pedigrees Squares represent males and circles represent females Horizontal lines connecting a male and female represent mating Vertical lines extending downward from a couple represent their children

Oldest individuals are found at the top of the pedigree Shade in the symbol of all individuals that possess this trait If an individual died due to the trait, put a slash through their symbol

Lethal Allele Dominant example: Huntington’s Recessive example: Cystic Fibrosis Alleles that cause an organism to die only when present in homozygous condition are called lethal alleles. The gene involved is considered an essential gene.

Developing Conclusions About Different Modes of Inheritance

Autosomal Dominant Tt tt Tt tt Shaded individuals HAVE the trait and must have the dominant allele (at least one capital letter). Un-shaded individuals do NOT have the trait. They are homozygous recessive (two lower case letters). The traits are often present in every generation. tt Tt Tt tt

Autosomal Recessive Tt Tt tt T? Shaded individuals HAVE the trait and they are homozygous recessive (two lower case letters). Un-shaded individuals do NOT have the trait and must have the dominant allele (at least one capital letter). The traits are often present in every other generation Tt Tt tt T?

Practice #1 Is the pedigree for a dominant or recessive trait? Give the genotypes for each individual.

Practice #2 Is the pedigree for a dominant or recessive trait? Give the genotypes for each individual