makkah

THE STEPS WHEN INTERPRETING
A PEDIGREE CHART
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Determine if the pedigree chart shows an autosomal or Xlinked disease.

 If most of the males in the pedigree are affected, then the disorder is X-linked
 If it is a 50/50 ratio between men and women the disorder is autosomal.

INTERPRETING A PEDIGREE
CHART


Determine whether the disorder is dominant or recessive.  If the disorder is dominant, one of the parents must have the disorder.
 If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous.

Pedigree showing transmission and expression of a mitochondrial trait. Note that transmission occurs only through females. Rules of Inheritance
Autosomal Recessive
•Appears in both sexes with equal frequency
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Trait tend to skip generations
• Affected offspring are usually born to unaffected parents
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When both parents are hetrozygout, approx. 1/4 of the progeny will be affected
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Appears more frequently among the children of consanguine marriages

Rules of Inheritance
Autosomal Dominant
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Appears in both sexes with equal frequency
• Both sexes transmit the trait to their offspring
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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 other parent is unaffected, approx. 1/2 of the offspring will be affected
• Unaffected parents do not transmit the trait

Rules of Inheritance
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X-Linked Dominant
Both males and females are affected; often more females than males are affected
Does not skip generations.
• Affected sons must have an affected mother;
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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 their daughters Rules of Inheritance

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