PEDIGREE PRACTICE: In the exercises below, assume that the trait in question (shaded) is a genetic
disease or abnormality. We will search for the following patterns of inheritance in each pedigree:
 autosomal dominant or recessive (chromosomes 1-22)
 X-linked recessive (the X chromosome on the 23rd pair)
AUTOSOMAL TRAITS/DISORDERS
The pedigree below is for a genetic disease or abnormality. We do not yet know if it is dominant or
recessive, but can easily figure this out! So, write the alleles above each individual using the letters “A”
and “a” as your alleles. Try both dominant and recessive to see which one works. If they both work,
then this pedigree would be inconclusive. In other words, there is not enough information in the
pedigree to show the inheritance pattern.
1.
2.
The shaded trait is ____________________.
The shaded trait is ____________________.
3.
4.
The shaded trait is ____________________.
The shaded trait is ____________________.
SEX-LINKED RECESSIVE TRAITS/DISORDERS:
We will determine if the pedigrees below can be for a trait that is X-linked recessive. Use the following
alleles: XA = normal Xa = genetic disease or abnormality Y = Y chromosome (males only)
1. Is it possible for the pedigree below to be for a
sex-linked recessive trait? _________
2. Is it possible for the pedigree below to be for a
sex-linked recessive trait? _________
3. Is it possible for the pedigree below to be for a
sex-linked recessive trait? _________
4. Is it possible for the pedigree below to be for a
sex-linked recessive trait? _________
5. Is it possible for the pedigree below to be for a
sex-linked recessive trait? _________
APPLICATION OF PEDIGREE ANALYSIS:
The conclusions about inheritance (above) can be used to help analyze pedigrees. For each pedigree
below, tell if the trait can be autosomal dominant, autosomal recessive, and X-linked recessive by
completing the chart with checkmarks.
Type of Inheritance
Possible Not possible
Autosomal Dominant
Autosomal Recessive
Sex-linked Recessive