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Pedigrees Basic rules

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Pedigrees; Basic rules. Each generation is assigned a Roman numeral, beginning with the earliest ... Pedigrees; basic rules. Some basic assumptions. everyone is ... – PowerPoint PPT presentation

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Title: Pedigrees Basic rules


1
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
2
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

3
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...
4
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.
5
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!

6
I
II
III
7
A a
A a
Aa
Aa
8
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9
Aa
Aa
?
aa
10
Cystic fibrosis transmembrane conductance
regulator
Cystic fibrosis Recessive 1/4000 Caucasians
11
Amyotrophic lateral sclerosis Lou Gehrigs
disease dominant 1/50,000 (?)
?
12
Xeroderma pigmentosum inability to repair UV
damage to DNA skin tumors, death
13
PKU
14
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

15
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

16
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

17
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

18
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