Pedigree Analysis

What’s in YOUR family tree?

Pedigree Analysis

Pedigree Analysis

In humans, pedigree analysis is an important tool for studying inherited diseases

Pedigree analysis uses family trees and information about affected individuals to:

• figure out the genetic basis of a disease or trait from its inheritance pattern

• predict the risk of disease in future offspring in a family (genetic counseling)

Today….

How to read pedigrees

Determining basic patterns of inheritance1. autosomal recessive2. autosomal dominant3. X-linked recessive4. X-linked dominant (very rare)

Applying pedigree analysis – practice

Looking at the Blue People of Troublesome Creek

Pedigree Symbols

1. Autosomal recessive pedigree - cystic fibrosis

femalemale

affected individuals

1. Autosomal recessive traits

• Trait is rare in pedigree

• Trait often skips generations (hidden in heterozygous carriers)

• Trait affects males and females equally

Autosomal recessive diseases in humans:

Most common ones • Cystic fibrosis • Sickle cell anemia• Phenylketonuria (PKU)

These may be more common because their heterozygotes all give a survival advantage!!Cystic fibrosis heterozygotes are less

likely to die from choleraSickle cell heterozygotes are less likely to

die from malariaPKU heterozygotes (females) are less

likely to have miscarriages

Sickle Cell / Malaria Connection

2. Autosomal dominant pedigrees

• Trait is common in the pedigree

• Trait doesn’t skip generations

• Affected individuals transmit the trait to ~1/2 of their children (regardless of sex)

Autosomal dominant traits

There are few autosomal dominant human diseases, but some rare traits have this inheritance pattern

ex. achondroplasia (a sketelal disorder

causing dwarfism)

3. X-linked recessive pedigree

• Trait is rare in pedigree

• Trait skips generations

• Affected fathers DO NOT pass to their sons,

• Males are more often affected than females

Ex. Hemophilia in European royalty

X-linked recessive traits

•Red-green color blindness

•Hemophilia

•X-linked ichthyosis

4. X-linked dominant pedigrees

• Trait is common in pedigree

• Affected fathers pass to ALL of their daughters, but not their sons

• Doesn’t skip generations

X-linked dominant diseases

• X-linked dominant diseases are extremely unusual

• Often, they are lethal (before birth) in males and only seen in females

ex. incontinentia pigmenti (skin lesions)

ex. X-linked rickets (bones soften/deform)

Pedigree Analysis in real life

Keep in mind that pedigrees don’t always give the pattern of inheritance – many

factors (like the environment or multiple genes) might be involved!!

CHALLENGE #1

What is the pattern of inheritance? _______________What are IV-2’s odds of being a carrier? __________

CHALLENGE #2What is the inheritance pattern? _________________How do you know? ____________________________ __________________________________________

CHALLENGE #3

What is the inheritance pattern? __________________Identify the carriers: ___________________________How many children did I-1 and I-2 have? _____________

Now for CHALLENGE #4!!

• What is the inheritance pattern?

• What could have contributed to the frequency of the allele showing up?

CHALLENGE #4