PEDIGREE CHARTS

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PEDIGREE CHARTS

• A family history of a genetic condition

Pages 1-3 6-9 taken from Paul Billiet at the
following website saburchill.com/IBbiology/.../im
ages/05PEDIGREE CHARTS.ppt
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What is a pedigree chart?

• Pedigree charts show a record of the family of an
  individual
• They can be used to study the transmission of a
  hereditary condition
• They are particularly useful when there are large
  families and a good family record over several
  generations.

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Studying human genetics

• You cannot make humans of different types breed
  together
• Pedigree charts offer an ethical way of studying
  human genetics
• Today genetic engineering has new tools to offer
  doctors studying genetic diseases
• A genetic counsellor will still use pedigree
  charts to help determine the distribution of a
  disease in an affected family

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Sex on a Pedigree

• Males
• Females

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Connecting Lines

• Marriage horizontal line between two people
• Siblings horizontal line above boxes
• Twins
• Fraternal
• Identical

Children are listed from youngest to oldest (left
to right)
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Symbols used in pedigree charts

• Normal male Affected male
• Normal female Affected
  female
• or autosomal carrier
  (heterozygote )
• x-linked carrier
• or deceased

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Organizing the pedigree chart

• A pedigree chart of a family showing 20
  individuals

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Organizing the pedigree chart

• Generations are identified by Roman numerals

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Organizing the pedigree chart

• Individuals in each generation are identified by
  Arabic numerals numbered from the left
• Therefore the affected individuals are II3, IV2
  and IV3

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Reading a Pedigree Chart

• Autosomal or x-linked trait?
• If the affected are mostly males then the trait
  is x-linked
• If the affected is a fairly even ratio between
  males and females then the trait is autosomal

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Autosomal or X-linked?

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Autosomal

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Determining Dominant or Recessive Trait?

• If the disorder is dominant one of the parents
  must have the disorder
• If the disorder is recessive then neither of the
  parents HAS to have the trait because they are
  heterozygous. However one of both may have the
  disorder

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Dominant or recessive?
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Dominant
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Dominant or Recessive?
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Recessive
Some times carriers are not listed as a half
filled in square/circle. You must interpret the
pedigree
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Pedigrees

• Remember.
• you must READ and INTERPRET the pedigree.