3-1 patterens of inheritance
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THE STEPS WHEN INTERPRETING
A PEDIGREE CHART ! Determine if the pedigree chart shows an autosomal or X-
linked disease.
! If most of the males in the pedigree areaffected, then the disorder is X-linked
! If it is a 50/50 ratio between men andwomen the disorder is autosomal.
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NTERPRETING A PEDIGREE
CHART ! Determine whether the disorder is dominant or
recessive.
! If the disorder is dominant, one of theparents must have the disorder.
! If the disorder is recessive, neitherparent has to have the disorder becausethey can be heterozygous.
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Pedigree showing transmission and
expression of a mitochondrial trait. Notethat transmission occurs only throughfemales.
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Rules of Inheritance
Autosomal Recessive Appears in both sexes with equal frequency Trait tend to skip generations
Affected offspring are usually born tounaffected parents When both parents are hetrozygout,approx. 1/4 of the progeny will be affected
Appears more frequently among thechildren of consanguine marriages
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Rules of Inheritance
Autosomal Dominant Appears in both sexes with equal frequency Both sexes transmit the trait to their offspring Does not skip generations Affected offspring must have an affected parent
unless they posses a new mutation When one parent is affected (het.) and the otherparent is unaffected, approx. 1/2 of the offspring
will be affected Unaffected parents do not transmit the trait
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Rules of InheritanceX-Linked Dominant
Both males and females are affected; often morefemales than males are affected
Does not skip generations. Affected sons must have an affected mother; affected daughters must have either an
affected mother or an affected father Affected fathers will pass the trait on to all their
daughters Affected mothers if heterozygous will pass the
trait on to 1/2 of their sons and 1/2 of theirdaughters
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Rules of Inheritance
X-Linked Recessive More males than females are affected Affected sons are usually born to unaffected
mothers, thus the trait skips generations Approximately 1/2 of carrier mothers sons are
affected
It is never passed from father to son All daughters of affected fathers are carriers
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Rules of Inheritance
Mitochondrial Trait is inherited from mother only All children of a mother are at risk to be
affected or carriers
Y-Linked Dominant Only males are affected It is passed from father to all sons It does not skip generations
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Example
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Example 1
X-linked recessiveHemophilia
Only males are affected and sons do not share thephenotype of their father - Thus X-linkedExpression of hemophilia skips generations:
RECESSIVE
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Example 2
X-Linked DominantEvery Generation: Dominant
Father passes on to only daughters
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Example 3
Autosomal RecessiveAffected individual from
unaffected parents
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Example 4
Autosomal recessiveExpressed in both sexes at approximately
equal frequency: AUTOSOMALNot expressed Autosomal Recessive in every
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Example 5
Autosomal DominantIn every generation:DOMINANT
Equal in Males and Females:
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Example 6
Autosomal DominantAppears equally In both sexesso autosomal
In every generation so
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Example 7
Y-LinkedOnly males are affected
All sons of affected
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Example 8
X-Linked Dominant
Every generation: DOMINANT
Daughters of affected males are affected
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Example 9
Autosomal DominantIn every generation: DOMINANT
oth ale and e ale a ected:
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Example 10
MitochondrialAll children at risk
Father doesnt pass it along to
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Example 11
AutosomalRecessive
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Example 12
MitochondrialInheritance
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Example 13
Autosomal dominantIn every generation: DOMINANT In males and females: Autosomal
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Example 14
Mitochondrial InheritanceFathers dont transmit, just
mothers
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Example 15
X-linkedRecessive
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The End
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