5.6 Pedigrees
Notes
A pedigree is a family tree that shows how a trait is inherited.
- Squares = males, circles = females. Shaded = has the trait; half-shaded = carrier (if shown).
- A horizontal line joining a male and female is a mating; vertical lines lead to children.
- Autosomal recessive: can skip generations; two unaffected parents can have an affected child.
- Autosomal dominant: every affected person usually has an affected parent; it does not skip generations.
- X-linked recessive: mostly males affected, often passed from a carrier mother to a son.
Practice
Two parents without a trait have a child with the trait. The trait is most likely:
Both parents must be hidden carriers of the recessive allele.
In a pedigree, a trait appears in every generation, and every affected child has at least one affected parent. The trait is most likely:
Dominant traits show whenever one copy is present, so they rarely skip generations.
In a pedigree, what does a shaded square represent?
Squares are males and shading means the person has the trait.
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