Download - How to Analyze a Pedigree
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Honors Biology Genetics!
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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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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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1. If two affected people have an unaffected child.
2. If every affected person has an affected parent.
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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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1 2 3 4 5 6 7 8 9 10
1 2
I
1 2 3 4 5 6
II
III
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1. If two unaffected people have an affected child
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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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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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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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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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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