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Paediatric

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Genetic Disorders

Question
7 out of 49
 

A parent is homozygous and a parent heterozygous for an autosomal recessive gene. What will be the outcome- (LQ)



A 75% children affected

B No child affected, but all are carriers

C 50% children affected, rest are carriers

D 25% children affected, rest are carriers

Ans. C

50% children are affected, Rest are carriers

Autosomal recessive disorders

o Autosomal recessive disorders are manifested in homozygous state,

i.e. when both alleles at a given gene locus are mutant.

o There may be following five situations -

1. One parent is carrier and the other is normal + 50% of child will be carrier.

Aa aa

Aa Aa aa aa

2. Both the parents are carrier + 25% children will be affected, 50% will be carrier and 25% will be normal.

Aa Aa

AA Aa Aa aa

3. One parent is affected and other is carrier 50% of child will be affected, 50% will be carrier.

AA Aa

AA AA Aa Aa

4. Both parents are affect + 100% children will be affected.

AA AA

AA AA AA AA

5. One parent is affected and one is normal All will be carrier

AA aa

Aa Aa Aa Aa

Note - I have given the percentage of genotypically affected children.

o Affection of phenotype will be different because all carrier will be phenotypically normal (as autosomal recessive disease is manifested only in Homozygous state).

o So in 1st situation all child (100%) will be phenotypically normal, 2nd situation 75% child will be phenotypically normal and in 3rd situation 50% will be normal in 4th situation no child will be normal and in 5th situation all will be normal.

o But you remember the percentage of affected children for which there is no confusion.

Genetic Disorders Flashcard List

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