Key Knowledge:
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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 mean an individual is affected by a condition, while an unshaded symbol means they are unaffected
- A horizontal line between man and woman represents mating and resulting children are shown as offshoots to this line
- Generations are labeled with roman numerals and individuals are numbered according to age (oldest on the left)
Autosomal Inheritance
Dominant and recessive disease conditions may be identified only if certain patterns occur (otherwise it cannot be confirmed)
Autosomal Dominant
- If both parents are affected and an offspring is unaffected, the trait must be dominant (parents are both heterozygous)
- All affected individuals must have at least one affected parent
- If both parents are unaffected, all offspring must be unaffected (homozygous recessive)
Autosomal Recessive
- If both parents are unaffected and an offspring is affected, the trait must be recessive (parents are heterozygous carriers)
- If both parents show a trait, all offspring must also exhibit the trait (homozygous recessive)
X-Linked Inheritance
It is not possible to confirm sex linkage from pedigree charts, as autosomal traits could potentially generate the same results
- However certain trends can be used to confirm that a trait is not X-linked dominant or recessive
X-linked Dominant
- If a male shows a trait, so too must all daughters as well as his mother
- An unaffected mother cannot have affected sons (or an affected father)
- X-linked dominant traits tend to be more common in females (this is not sufficient evidence though)
X-linked Recessive
- If a female shows a trait, so too must all sons as well as her father
- An unaffected mother can have affected sons if she is a carrier (heterozygous)
- X-linked recessive traits tend to be more common in males (this is not sufficient evidence though)
