Transcript How to Analyze a Pedigree

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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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.
Look for:
 Trait in every generation
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Once leaves the pedigree does not return
Every person with the trait must have a parent with
the trait
Males and females equally affected
Look for:
 Skips in generation
 Unaffected parents can have affected children
 Affected person must be homozygous
 Males and females affected equally
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