Download Pedigree Charts

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.