How to Analyze a Pedigree

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How to Analyze a Pedigree

• Honors Biology Genetics!

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Whats a Pedigree?

• Pedigree is a family tree used to study how
  particular human traits are inherited.
• It is analyzed using logic and the Mendelian laws

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Goals of a Pedigree

• 1. Determine the mode of inheritance dominant,
  or recessive, sex-linked or autosomal
• 2. Determine the probability of an affected
  offspring for a given cross.

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Basic Symbols
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More Symbols
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Dominant Pedigree?

• 1. If two affected people have an unaffected
  child.
• 2. If every affected person has an affected
  parent.

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Assigning Genotype for Dominant

• 1. All unaffected are dd.
• 2. Affected children of an affected parent and an
  unaffected parent must be heterozygous Dd,
  because they inherited a d allele from the
  unaffected parent.
• 3. The affected parents of an unaffected child
  must be heterozygotes Dd, since they both passed
  a d allele to their child. (also called carriers)

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Dominant Autosomal Pedigree
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Recessive Pedigree?

• 1. If two unaffected people have an affected child

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Assigning Genotype for Recessive

• 1. all affected are rr.
• 2. If an affected person (rr) mates with an
  unaffected person, any unaffected offspring must
  be Rr heterozygotes, because they got a r allele
  from their affected parent.
• 3. If two unaffected mate and have an affected
  child, both parents must be Rr heterozygotes.

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Autosomal Dominant

• Look for
• Trait in every generation
• Once leaves the pedigree does not return
• Every person with the trait must have a parent
  with the trait
• Males and females equally affected

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Autosomal Dominant
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Autosomal Recessive

• Look for
• Skips in generation
• Unaffected parents can have affected children
• Affected person must be homozygous
• Males and females affected equally

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Autosomal Recessive
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Sex-Linked Dominant

• Look for
• More males being affected
• Affected males passing onto all daughter
  (dominant) and none of his sons
• Every affected person must have an affected
  parent

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Sex-Linked Recessive

• Look for
• More males being affected
• Affected female will pass onto all her sons
• Affected male will pass to daughters who will be
  a carrier (unless mother also affected)
• Unaffected father and carrier mother can produce
  affected sons

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Sex-linked recessive