“All In The Family”Pedigree Analysis
What is a pedigree?
• Pedigree charts show a record of the family of an individual.
• They can be used to study the transmission of a hereditary condition.
• Useful when there are large families and a good family record over several generations.
Why use one?It is a Key Tool in Human Genetics
It is like puzzle-building – you try assigning potential genotypes until the pieces fit
Symbols Used
• Normal male
• Affected male
• Normal female
• Affected female
• Marriage
A marriage with five children, two daughters and three sons. The middle son is affected by
the condition.
Eldest child Youngest child
People who have children together are connectedby a horizontal line:
Their children are connected to them with a vertical line. Siblings are connected as shown.
Organizing a Pedigree Chart
– Generations are identified by Roman numerals
I
II
III
IV
And more organizing…
• Individuals in each generation are identified by Arabic numerals numbered from the left
• Therefore the affected individuals are II3, IV2 and IV3I
II
III
IV
Patterns of recessive traits
• may appear to “skip” generations
• most children of normal and affected parents are normal– AA x aa ---> Aa
• all children of two affected parents will be affected– aa x aa ---> aa
A Pedigree of a Recessive Human Trait
Note: Trait can appear in offspring of parents without the trait. Heterozygotes who do not show the trait are termed carriers.
Patterns of dominant traits
• at least one parent must be affected in order for children to be affected– Aa x aa
• normal parents will always produce normal offspring– aa x aa ---> aa
A Pedigree of a Dominant Human Trait
Note: Trait appears in every gen. and ½ the offspring of an affected heterozygote are expected to show the trait.
So, let’s practice…
Background: • PKU is a recessive disease where sufferers
lack a protein needed to properly digest foods. It can be fatal if untreated.
In EduCreations…
KeyH = healthyh = PKU
1) Manny and Rosa are married and both are healthy.2) They have 3 children.3) Their oldest child, Jacob, has a recessive disorder called
PKU.4) Their middle child Erica and their youngest Matthew are
healthy.
Hint: Fill in what you know first!
If only it was that simple! The next generation…
Key
H = healthy
h = PKU
5. Erica meets Moe at college and they get married.
6. Erica and Moe have 2 daughters.
7. Their youngest daughter Jamie shows signs of PKU while Amy does not.
• Fill in the genotypes of the four individuals. (start with what you know)
Sickle cell anemia (recessive) pedigree
hh
hh hh
Key
H = Healthy
h = Sickle cell disease
Hint: 3 unknown
Start with the shaded circles and squares. They must be hh because they have the disease.
Sickle cell anemia (recessive) pedigree
hh
hh hh
hh
H
H HHH
HH H
H
Key
H = Healthy
h = Sickle cell disease
Hint: 3 unknown
Everyone else is healthy so they have at least one capital H.
Sickle cell anemia (recessive) pedigree
hh
hh hh
hh
H
H HHH
HH H
H
Key
H = Healthy
h = Sickle cell disease
Hint: 3 unknown
George must be Hh because he fathered Wilma and Tom. If he was HH, none of his kids would have the disease.
h
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