ishu
Forum Newbie
Topics: 9
Posts: 30
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a 30 yr old man phenotypically normal, but two of his siblings died from infantile Tay-sachs disease, an autosomal recessive condition that is lethal by the age 5. what is the risk that this man is a heterozygous carrier of the disease-causing mutation?
please explain the answer
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| macTT
Forum Senior
Topics: 32
Posts: 86
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I would say 100%
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| NE
Forum Guru
Topics: 53
Posts: 504
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if the kids have the disease means they have 2 defective genes- one from the father (carrier if is phenotypically healthy) and one from the mother ( disease or carrier). So the probability is 100%.
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| Norris
Forum Newbie
Topics: 1
Posts: 2
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Do you guys know nothing!
The parents must both be carriers if they have each passed on a recessive allele to the two sufferer children. But being carriers means they both have one dominant, normal allele, which could have been passed on to the man.
He has a one third probability of having two normal dominant alleles.
He is either homozygous dominant, heterozygous (with recessive allele from mum), or heterozygous (with recessive allele from dad).
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| medocuk
IM-RES
Topics: 26
Posts: 1,499
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Ha ha ha..No I guess we don't know so much.Thanks Norris. 
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| Ancylostoma
Forum Guru
Topics: 42
Posts: 642
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I have done a question similar to this, normally in a autosomal recessive person the chance the ratios is 1:2:1, 1 affected, 2 carriers, 1 not affected. Thats if we assume that two carrier mate. And that what we do because the chance of two homozygous recessive individuals mating is extremely low, and that would mean he has the disease. Which is not the case. Finally, since he does not have the disease , we can eliminate that choice. That means the only possibilities left are 2 carrier or unaffected. Thus the probability of being a carrier is 2/3. Hope this helps. Go over it again , you will understand the question more clearly now.
Edited by Ancylostoma on 12/17/06 - 08:21 PM
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| laura81
Forum Elite
Topics: 32
Posts: 175
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i agree with you ancylostoma the probab. its 2/3 cause he is phenotipically normal.
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