Download Pedigrees

Pedigrees
CP Biology
Genetics Unit
What is a Pedigree?
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A diagrammatic tool used by
geneticists to show the family
history of how a trait is inherited.
In other words, similar to a family
tree but looks at one trait/disorder
only.
How is a Pedigree Helpful?
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Tracing a genetic disorder through a
family over several generations.
Determining the possibility of a
genetic disorder being passed to
offspring.
Determining the possibility of
parents being carriers of a genetic
disorder.
What are Carriers?
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Carriers are heterozygous
individuals who carry the recessive
gene for the disorder.
Carriers do not show symptoms of
the disorder.
They can pass the allele for the
disorder to their offspring.
What can Scientists Determine from a
Pedigree?
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If the trait is dominant or recessive
If the trait is heterozygous or
homozygous
If the disorder is autosomal (carried
on an autosome) or if it is sexlinked (carried on the X
chromosome)
Autosomal Disorders
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Remember, an autosome is a nonsex chromosome: chromosome #1
– 22, NOT pair #23
The trait can be dominant or
recessive.
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Dominant – must have parents with the
disorder
Recessive – heterozygous parents can
have offspring with a recessive disorder
Example: Cystic Fibrosis (recessive)
Sex-Linked Disorders
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Most sex-linked disorders are recessive.
If a trait is sex-linked, it is seen primarily
in males.
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This is because almost all sex-linked
disorders are located on the X chromosome.
Since males only have one X chromosome,
the trait shows up.
Females have two X chromosomes, they can
have one dominant (normal) allele and one
recessive allele.
How to Construct a Pedigree
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Horizontal lines indicate matings.
Vertical lines indicate offspring,
arrange in order of their birth (left
to right)
Squares = males
Circles = females
Shaded in boxes = affected
individuals