3-1 patterens of inheritance

8/13/2019 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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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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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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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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3-1 patterens of inheritance

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