Pedigree Analysis

• 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

•
•
•
• 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 connected by a horizontal line:
Their children are connected to them with a vertical line. Siblings are connected as shown.

– Generations are identified by Roman numerals
I
II
III
IV

• Individuals in each generation are identified by Arabic numerals numbered from the left
• Therefore the affected individuals are
II3 , IV2 and IV3
I
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.

Background:
• PKU is a recessive disease where sufferers lack a protein needed to properly digest foods. It can be fatal if untreated.

Key
H = healthy h = 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!

Key
H = healthy h = PKU
If only it was that simple!
The next generation…
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
Hint: 3 unknown hh hh hh
Start with the shaded circles and squares.
They must be hh because they have the disease.
Key
H = Healthy h = Sickle cell disease

Sickle cell anemia (recessive) pedigree
Hint: 3 unknown H hh
H
H hh
H
H
H
H hh H H
Everyone else is healthy so they have at least one capital H.
hh
Key
H = Healthy h = Sickle cell disease

Sickle cell anemia (recessive) pedigree
Hint: 3 unknown H h hh
H
H hh
H
H
H
H hh H H
George must be
Hh because he fathered Wilma and Tom. If he was HH, none of his kids would have the disease.
Key
H = Healthy hh h = Sickle cell disease