asmi
Forum Hero
Topics: 1043
Posts: 4,609
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35 yr old man who is phenotypically normal but his 2 son's died of tay sach's disease .What is the risk that this man is heterogyzous carrier of the disease ?
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| usmleasr
Forum Guru
Topics: 105
Posts: 970
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100%??
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| asmi
Forum Hero
Topics: 1043
Posts: 4,609
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nope
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| oddissy4u
Forum Guru
Topics: 107
Posts: 389
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50%?
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| asmi
Forum Hero
Topics: 1043
Posts: 4,609
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the answer is 2/3 or 66%
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| oddissy4u
Forum Guru
Topics: 107
Posts: 389
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hows tht?
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| asmi
Forum Hero
Topics: 1043
Posts: 4,609
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:arrow: his parents both should be carrier since he produced two children with the disease. :arrow: since he is not affected,this excludes 1/4 (which is the probablity of inheriting two copies of disease allele).
:arrow: his risk of inheriting a copy of disease gene at conception is 1/2 but since he is phenotypically normal means he cannot have inheritied copies from both parents .
:arrow: so he should inherit a copy from father or a copy from mother or shouldnot get any .
:arrow: two of the above possiblities leads to heterozygosity...thus his risk of being a carrier is 2/3
I am really having tough time with these stupid Q's from genetics :cry:
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| oddissy4u
Forum Guru
Topics: 107
Posts: 389
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u r atleast able to solve them,i m not getting even wth explanations ......genetics is driving me crazy :roll:
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| bobby
Forum Guru
Topics: 136
Posts: 569
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i thought i was the only person having tough time with genetics and all those calculations etc....
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if you haven't any charity in your heart, you have the worst kind of heart trouble.
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| asmi
Forum Hero
Topics: 1043
Posts: 4,609
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no boby its the same problem with everyone except few people like meg ,mjl etc
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| Malaysian
Forum Guru
Topics: 28
Posts: 778
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I think its 100% as mentioned by usmleasr.
Since the 2 kids got the disease their genotype(a,a) would have been contributed by 1 from the father and 1 from the mother.And so the father is 100% a carrier and there is no chance of him being a normal genotype.He cannot be having the disease because he's already 35years.The answer given by asmi is incorrect.
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| Alina T
Forum Elite
Topics: 17
Posts: 388
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yes, that's what I would have chosen 100% also.
I don't really understand asmi's explanation. is there something that I'm missing? coz it seems that everybody agreed with it.
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There are 3 types of people: those who make things happen, those who watch things happen, and those who wonder what happened.
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