Title: Pedigrees Basic rules
1Pedigrees 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
2Pedigrees 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...
4People 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.
5Pedigrees 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!
6I
II
III
7A a
A a
Aa
Aa
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9Aa
Aa
?
aa
10Cystic fibrosis transmembrane conductance
regulator
Cystic fibrosis Recessive 1/4000 Caucasians
11Amyotrophic lateral sclerosis Lou Gehrigs
disease dominant 1/50,000 (?)
?
12Xeroderma pigmentosum inability to repair UV
damage to DNA skin tumors, death
13PKU
14Patterns 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
15Patterns 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
16Patterns 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
17Patterns 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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