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Old 06-07-2011
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Genetics The risk of being heterozygous!

A 30-year-old man is phenotypically normal, but two of his siblings died from infantile Tay-Sachs disease. What is the risk that this man is a heterozygous carrier of the disease-causing mutation?

A 1/4
B 1/2
C 2/3
D 3/4
E not elevated above that of the general population



---------------------------------------------------------------------

Tay–Sachs


Defeciency: Hexosaminidase A

Accumulation: GM2 ganglioside

- Amaurotic familial idiocy
- Blindness
- Cherry-red spot in macula
- Death < 4 y/o
- HEXA gene mutation on chromosome 15
- Ashkenazi Jews

Last edited by m82_ghasemi; 06-07-2011 at 03:04 PM.
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Old 06-07-2011
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Default

C) 2/3

Parents have to both be carriers since brothers have disease


Therefore possibilities are:

1/4 TT
2/4 Tt
1/4 tt

But since we know the patient does not have the disease, we can rule out tt

We are left with 2/3 chance of being carrier
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  #3  
Old 06-07-2011
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As apx85 answered, C is correct.
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