Pedigrees Basic rules

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Pedigrees Basic rules

• Each generation is assigned a Roman numeral,
  beginning with the earliest
• Individuals w/in generations are assigned Arabic
  numerals, beginning with the left

I II
1
2
1
2
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Pedigrees Basic rules

• Females circles
• Males squares
• Open circles/squares unaffected individuals
• Filled in circles/squares affected individuals
• dots, crosses, etc. may be used if gt one trait
  studied

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unaffected female
affected female
female affected by two traits
unaffected male
male affected by one trait
male affected by second, but not first trait
And more...
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People who have children together are
connected by a horizontal line
Their children are connected to them with a
vertical line. Siblings are connected as shown.
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Pedigrees basic rules

• Some basic assumptions
• everyone is telling the truth!
• unless direct evidence to contrary, assume
  individuals marrying into pedigree are as normal
  as possible
• normal depends on whether the trait is dominant
  or recessive
• assume traits are rare!

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I
II
III
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A a
A a
Aa
Aa
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Aa
Aa
?
aa
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Cystic fibrosis transmembrane conductance
regulator
Cystic fibrosis Recessive 1/4000 Caucasians
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Amyotrophic lateral sclerosis Lou Gehrigs
disease dominant 1/50,000 (?)
?
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Xeroderma pigmentosum inability to repair UV
damage to DNA skin tumors, death
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PKU
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Patterns of recessive traits

• may appear to skip generations
• most children of normal and affected parents are
  normal
• AA x aa ---gt Aa
• all children of two affected parents will be
  affected
• aa x aa ---gt aa

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Patterns of recessive traits

• normal parents may produce affected offspring
• Aa x Aa ---gt 3/4 normal 1/4 affected
• affected children often result when parents are
  blood relatives

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Patterns of dominant traits

• trait tends to appear each generation
• normal and affected individual expected to
  produce normal and affected children (approximate
  11 ratio)
• Affected individuals generally heterozygous if
  rare trait
• Aa x aa ---gt 1/2 Aa 1/2 aa

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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 ---gt aa

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