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Prep4USMLE Forum » USMLE Step 1 Forum » Histology & Molecular Biology

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5 Posts

Geroo
Forum Guru

Topics: 114
Posts: 799

12/19/05 - 10:10 PM

30 years old man is phenotypically normal but two of his sibling died from infantile tay-sachs disease that is lethal by age of five.what is the risk that this man is heterozygous carrier of that disease
A) 1/4
B) 1/2
C) 2/3
D) 3/4
E) same risk as of general population.

Edited by Geroo on 12/19/05 - 10:17 PM

roopashri
Forum Elite

Topics: 16
Posts: 190

12/20/05 - 07:35 AM

since 2 bros died of taysachs.. it means parents were carriers aA. This man is normal so aa is ruled out. and can be only AA, Aa, Aa genotype.

Out of the 3, 2 are carriers. so answer is 2/3... am i right?

sturge_weber
Forum Guru

Topics: 77
Posts: 1,042

12/20/05 - 09:54 AM

2/3...

as Roopa mentioned, he is not disased his chance of being aa is eliminated, hence he is out of three possiblities, Aa, Aa, AA... out of these the chances he is a carrier, is 2/3

Geroo
Forum Guru

Topics: 114
Posts: 799

12/20/05 - 08:28 PM

yes you got it guys

RayBerg
Forum Senior

Topics: 32
Posts: 150

12/31/05 - 03:27 AM

I guess the key to this q was to know that Tay Sachs is an autosomal recessive disorder.

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