“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