Transcript In The Family

“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 connected
by 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 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.
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…
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!
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
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
H
H
hh
hh
H
H
H
hh
Everyone else
is healthy so
they have at
least one
capital H.
H
H
hh
Key
H = Healthy
H
h = Sickle cell disease
Sickle cell anemia (recessive) pedigree
Hint: 3 unknown
H
H
Hh
hh
hh
H
H
H
H
hh
George must be
Hh because he
fathered Wilma
and Tom. If he
was HH, none
of his kids
would have the
disease.
H
H
hh
Key
H = Healthy
h = Sickle cell disease