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Pedigrees
What is a pedigree?
• A family tree that shows the passage of a
trait
Following Traits in a Pedigree
Steps:
1. Fill in all recessive individuals
2. Determine unknowns
An Example
The trait we are tracking is dominant.
Determine the genotype of individuals
1, 3, 6, 7
This pedigree is for lung disease. The trait is recessive
What is the genotype for individuals
2, 4, 10, 12 and 13
1
5
2
3
4
7
6
8
9
13
12
14
15
16
10
11
DETERMINING MODE OF
INHERITANCE ON A PEDIGREE
Modes of Inheritance
• Autosomal Recessive
• Autosomal Dominant
• Sex-linked recessive
• Sex-linked dominant
Autosomal Dominant vs. Recessive
• Things to look for
– Autosomal Recessive traits
• Occur less often
• Skip generations
• Two parents with the trait MUST give the trait to
their kids
– Autosomal Dominant Traits
• Occurs more often
How can we figure it out
• Look for sections of the family that the
parents either both
– have the trait
– do not have trait
First assume the trait dominant (assume all
dominant people are heterozygous) and see if
it possible
Then assume it is recessive (assume all
dominant people are heterozygous) and see if
it possible
For each of the following determine
if it can be a recessive trait and/or a
dominant trait
Sometimes____________
A bigger one
1. Is it autosomal recessive or autosomal dominant? How do you know?
2. Write the genotypes of the people you know
Another bigger one
1. Is it autosomal recessive or autosomal dominant? How do you know?
2. Write the genotypes of the people you know
What if you cannot find parents that
either don’t have it or do have it.
Cry!
Traits that occur less often are usually recessive
Traits that skip generations are usually recessive
To be sure you have to go through the entire
pedigree and assume each possibility
FOR EXAMPLE
Another Example
Recessive Sex-Linked
•
•
•
More men will be affected
an affected female will transmit the trait
to all male children
In order to have an affected female the
dad must have the trait
Can these pedigrees be recessive
sex-linked?
Other Types of Inheritance
•
Sex-linked dominant
•
•
Y linked:
•
•
If Dad has the trait, all the daughters must have the
trait
If Dad has the trait, all the sons must have the trait
Mitochondrian Genes
•
An affected mother will give the trait to all children