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Pedigree Analysis
What’s in YOUR family tree?
Pedigree Analysis
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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)
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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
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Pedigree Symbols
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1. Autosomal recessive pedigree - cystic fibrosis
femalemale
affected individuals
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1. Autosomal recessive traits
• Trait is rare in pedigree
• Trait often skips generations (hidden in heterozygous carriers)
• Trait affects males and females equally
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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
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Sickle Cell / Malaria Connection
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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)
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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)
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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
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Ex. Hemophilia in European royalty
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X-linked recessive traits
•Red-green color blindness
•Hemophilia
•X-linked ichthyosis
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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
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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)
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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!!
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CHALLENGE #1
What is the pattern of inheritance? _______________What are IV-2’s odds of being a carrier? __________
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CHALLENGE #2What is the inheritance pattern? _________________How do you know? ____________________________ __________________________________________
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CHALLENGE #3
What is the inheritance pattern? __________________Identify the carriers: ___________________________How many children did I-1 and I-2 have? _____________
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Now for CHALLENGE #4!!
• What is the inheritance pattern?
• What could have contributed to the frequency of the allele showing up?
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CHALLENGE #4