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Pedigree Charts
The family tree of genetics
What is a Pedigree?
• A pedigree is a chart of the genetic history of
family over several generations.
• Scientists or a genetic counselor would find out
about your family history and make this chart to
analyze.
Constructing a Pedigree
• Female
• Male
Connecting Pedigree Symbols
Examples of connected symbols:
• Married Couple/
couple with children
• Siblings
Example
• What does a pedigree chart look like?
Example of Pedigree Charts
• The Shaded means that person has that trait
Interpreting a Pedigree Chart
2. Determine whether the trait is dominant or
recessive. (remember: the dominant traits shows if
there is one or two, the recessive shows only if there
are two)
– If the trait is dominant, one of the parents must
have the trait.
– If the trait is recessive, neither parent has to have
the trait because they can be heterozygous.
Heterozygous vs. Homozygous
• Remember that an offspring gets one allele for
a trait from each parent – that’s 2 alleles
– If the alleles are the same, we say that offspring is
homozygous – the same
– If the alleles are different, we say the offspring is
heterozygous – different
Hetero & Homo zygous display
• An example: If the offspring has the dominant
trait for tallness (T) from one parent and the
recessive trait (t) from the other, then their
genotype is Tt and they are heterozygous.
(They are still tall)
• Some pedigrees split their circles and squares
into two and shade them according to
whether the individual is heterozygous or
homozygous.
AUTOSOMAL DOMINANT INHERITANCE
Approximately a 1:1 ratio of affected vs. unaffected progeny with one
affected parent.
Transmission can occur from
affected father to affected son.
Direct transmission from an
affected parent to an affected
child.
(Affected children always
have an affected parent.)
DOMINANT DISEASE
Huntington’s Disease
• Woody Guthrie
• Arlo Guthrie
• Children
Lobster Foot
Dominant allele -- you have the disease or you don’t
AUTOSOMAL RECESSIVE INHERITANCE
Affected parents can have affected offspring.
However, affected
children typically do
not have affected
parents.
Affected individuals
can be either male or
female.
RECESSIVE
DISEASE
• Albinism
• Achondroplasia
• Both parents can be
carriers to have an
affected child
• 2 affected parents will
usually produce an
affected child
Example of Pedigree Charts
• Dominant or Recessive? (Many or Few?)
Example of Pedigree Charts
• Dominant or Recessive? (Many or Few?)
More affected
males than
females.
Affected grandfather to grandson thru carrier
female.
SEX-LINKED
RECESSIVE TRAITS
Females do not
manifest the
disorder.
Example of Pedigree Charts
• Autosomal or Sex-Linked? (Males/Females)
Example of Pedigree Charts
• Autosomal or Sex-Linked? (Males/Females)
Summary
• Pedigrees are family trees that explain your
genetic history.
• Pedigrees are used to find out the probability
of a child having a certain trait in a particular
family.
Autosomal Dominant
Bent Pinky
Hand Fold
Dimples
Mid-digital hair
PTC Tasting
Bent Little
Finger
Widow’s Peak
Short Hallux
(Big Toe)
Finger
Length
Tongue Roll
Attached Earlobe
Tongue Flip
Tongue Fold
Unattached Earlobe
Hitchhiker’s Thumb
Ear Diagram
Ear Wax
Examples sex-linked
recessive traits:
COLOR
BLINDNESS