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 ExampleThe trait we are tracking is dominant. Determine the genotype of individuals

1, 3, 6, 7

This pedigree is for lung disease. The trait is recessiveWhat is the genotype for individuals

2, 4, 10, 12 and 13

1 2

987

65

43

1312

1110

14 15 16

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 traitFirst 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• If Dad has the trait, all the daughters must have the

trait

• Y linked:• If Dad has the trait, all the sons must have the trait

• Mitochondrian Genes• An affected mother will give the trait to all children