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Pedigree Charts The family tree of genetics Pedigree Charts I II III What is a Pedigree? u A pedigree is a chart of the genetic history of family over several generations. u Scientists or a genetic counselor would find out about your family history and make this chart to analyze. Constructing a Pedigree u Female u Male Connecting Pedigree Symbols Examples of connected symbols: u Fraternal twins u Identical twins Connecting Pedigree Symbols Examples of connected symbols: u Married Couple u Siblings Example u What does a pedigree chart look like? Symbols in a Pedigree Chart u Affected u X-linked u Autosomal carrier u Deceased Interpreting a Pedigree Chart 1. Determine if the pedigree chart shows an autosomal or X-linked disease. – If most of the males in the pedigree are affected the disorder is X-linked – If it is a 50/50 ratio between men and women the disorder is autosomal. Example of Pedigree Charts u Is it Autosomal or X-linked? Answer u Autosomal Interpreting a Pedigree Chart 2. Determine whether the disorder is dominant or recessive. – If the disorder is dominant, one of the parents must have the disorder. – If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous. Example of Pedigree Charts u Dominant or Recessive? Answer u Dominant Example of Pedigree Charts u Dominant or Recessive? Answer u Recessive Autosomal recessive traits • Trait is rare in pedigree • Trait often skips generations (hidden in heterozygous carriers) • Trait affects males and females equally v Most common ones • Cystic fibrosis • Sickle cell anemia • Phenylketonuria (PKU) • Tay-Sachs disease Autosomal dominant pedigrees • Trait is common in the pedigree • Trait is found in every generation • Affected individuals transmit the trait to ~1/2 of their children (regardless of sex) X-linked recessive pedigrees • Trait is rare in pedigree • Trait skips generations • Affected fathers DO NOT pass to their sons, • Males are more often affected than females X-linked recessive traits ex. Hemophilia in European royalty X-linked dominant pedigrees • Trait is common in pedigree • Affected fathers pass to ALL of their daughters • Males and females are equally likely to be affected X-linked dominant diseases • X-linked dominant diseases are extremely unusual • Often, they are lethal (before birth) in males and only seen in females ex. incontinentia pigmenti (skin lesions) ex. X-linked rickets (bone lesions) What is the inheritance pattern? What is the genotype of III-1, III-2, and II-3? What are the odds that IV-5 would have an affected son? III-1 has 12 kids with an unaffected wife 8 sons - 1 affected 4 daughters - 2 affected Does he have reason to be concerned about paternity? Summary u Pedigrees are family trees that explain your genetic history. u Pedigrees are used to find out the probability of a child having a disorder in a particular family. u To begin to interpret a pedigree, determine if the disease or condition is autosomal or X-linked and dominant or recessive.