Pedigree Charts

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A pedigree is a chart of the genetic history of a family over several generations

  • Males are represented as squares, while females are represented as circles
  • Shaded symbols means an individual is affected by a condition, while an unshaded symbol means they are unaffected
  • A horizontal line between a man and woman represents mating and resulting children are shown as offshoots to this line
  • Generations are labelled with roman numerals and individuals are numbered according to age (left to right)


Determining Mode of Inheritance

Autosomal Dominance

  • All affected individuals must have at least one affected parent
  • If two parents are unaffected, all offspring must be unaffected (homozygous recessive)
  • If two parents are affected, they may have offspring who are unaffected (if parents are heterozygous)


Autosomal Recessive

  • If two parents show a trait, all children must also show the trait (homozygous recessive)
  • An affected individual may have two normal parents (if parents are both heterozygous carriers)


X-Linked Dominance

  • If a male shows a trait, so must all daughters as well as his mother
  • The disorder is more common in females
  • It is not possible to conclusively confirm sex-linkage from pedigree charts 


X-Linked Recessive

  • If a female shows the trait, so must all sons as well as her father
  • The disorder is more common in males
  • It is not possible to conclusively confirm sex-linkage from pedigree charts 


Identifying Modes of Inheritance