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MHP
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07/05/06 - 10:46 AM

11. Phenylketonuria is an AR autosomal recessive disease. What is the probability that the asymptomatic brother or sister of a child with the disease is a heterozygous carrier?
A) 0
B) 1/4
C) 1/2
D) 2/3
E) ¾

navmed
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07/07/06 - 11:41 AM

study_ing
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07/09/06 - 12:28 AM

C for sure. (punnett square helps)

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robin082006
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07/09/06 - 12:43 AM

study-ing it is D

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study_ing
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07/09/06 - 02:21 AM

well if the sibling is ASYMPTOMATIC, they CANNOT be homozygotes. hence the denominator is 3, not 4.

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DrLooLi
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07/15/06 - 07:59 PM

It's D:
knowing that the sibling is asymptomatic makes them belong to the 75% asymptomatic offsprings.
of those 75% there's a 25% (1/3) chance of homozygous normal, and 50% (2/3) chance of heterzygous for the disease.
so, it's 2 out of 3 chances that they're going to be heterzygous.

Edited by DrLooLi on 07/16/06 - 12:35 AM

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