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  #1  
Old 05-24-2013
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Listening genetics

can anyone help me wi d solution?


a 30yr old man is phenotypically normal but two of his siblings died from infantile tay sachs ,an autosomal recessive.wat is d risk dat this man is a heterozygous carrier of d mutation?

my answer is 1/2 but actual answer is 3/4
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  #2  
Old 05-24-2013
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Originally Posted by roopa.loveurlife View Post
can anyone help me wi d solution?


a 30yr old man is phenotypically normal but two of his siblings died from infantile tay sachs ,an autosomal recessive.wat is d risk dat this man is a heterozygous carrier of d mutation?

my answer is 1/2 but actual answer is 3/4
Well my answer is also 1/2 not sure where they got the 3/4 from!
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  #3  
Old 05-24-2013
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ok...thanku...
im finding it really hard doin some of d questions..do u hv any suggestions hw i can improve in genetics?
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  #4  
Old 05-24-2013
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Originally Posted by roopa.loveurlife View Post
ok...thanku...
im finding it really hard doin some of d questions..do u hv any suggestions hw i can improve in genetics?
Kaplan genetics is enough I think
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Old 05-24-2013
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Hello,

I'm curious of which book give the correct answer as 3/4. If it's truly the correct answer, I would like to find out how to arrive at that answer. Thanks

I actually arrive at: there's 2/3 chance that he is a heterozygous carrier. Both his parent are heterozygous carriers. Since this is infantile Tay-sachs (not late on-set Tay sachs disease), and he doesn't manifested the disease at age 30, he's not a homozygous for the mutant alleles. So that leave 2/3 of being a heterozygous carrier and 1/3 chance of being not being a carrier. Thoughts?

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Originally Posted by roopa.loveurlife View Post
can anyone help me wi d solution?


a 30yr old man is phenotypically normal but two of his siblings died from infantile tay sachs ,an autosomal recessive.wat is d risk dat this man is a heterozygous carrier of d mutation?

my answer is 1/2 but actual answer is 3/4
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  #6  
Old 05-24-2013
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Originally Posted by brad89300 View Post
Hello,

I'm curious of which book give the correct answer as 3/4. If it's truly the correct answer, I would like to find out how to arrive at that answer. Thanks

I actually arrive at: there's 2/3 chance that he is a heterozygous carrier. Both his parent are heterozygous carriers. Since this is infantile Tay-sachs (not late on-set Tay sachs disease), and he doesn't manifested the disease at age 30, he's not a homozygous for the mutant alleles. So that leave 2/3 of being a heterozygous carrier and 1/3 chance of being not being a carrier. Thoughts?
Not convincing at all show us how u arrived at 2/3. U just stated 2/3 chance of being heterezygote. From where did u get that? Obviously u said it right that both parents are carriers . So that means in autosomal recessive inheritance when both parents are carriers then we hv 1/4 being affected, 1/4 not affected and 2/4 being carriers so where from ur 2/3.?
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Old 05-24-2013
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This is actually a good question stem,
So the key is in stem of the question "he's phenotypically normal" and "infantile Tay-sach disease".
Both both are het. carrier = possible genotype for children: AA, Aa, Aa, aa (A = normal allele, a = mutant allele). Since this is an infantile form of Tay-sach and he doesn't manifest the phenotype at 30 years old, he does not have it (cross out "aa"). His sibling died from the died from the disease further reinforced the fact that he can only be normal, or het. carrier (AA, Aa, and Aa). So the chance of him being a het carrier is 2/3.

I think there's a rule for it: Within the normal siblings of an affected individual the probability of being a carrier is 2/3.

***Caution, this does not work for all autosomal recessive diesease, especially a late manifesting one.
***Also, in the situation where if the question ask what are the chance of a unborn child in the same family being a heterozyous carrier then it's 1/2 (because in this case you can not eliminate the "aa" genotype)

Quote:
Originally Posted by nsesereso View Post
Not convincing at all show us how u arrived at 2/3. U just stated 2/3 chance of being heterezygote. From where did u get that? Obviously u said it right that both parents are carriers . So that means in autosomal recessive inheritance when both parents are carriers then we hv 1/4 being affected, 1/4 not affected and 2/4 being carriers so where from ur 2/3.?

Last edited by brad89300; 05-24-2013 at 12:47 PM.
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The above post was thanked by:
Braunwald (05-24-2013), nsesereso (05-24-2013), roopa.loveurlife (05-25-2013)
  #8  
Old 05-24-2013
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Correct Answer

2/3 is the ans fr me too.. dey r asking heterozygous fr d mutation n so 1/3 r homozygous n 2/3 heterozygous.
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  #9  
Old 05-24-2013
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Quote:
Originally Posted by brad89300 View Post
This is actually a good question stem,
So the key is in stem of the question "he's phenotypically normal" and "infantile Tay-sach disease".
Both both are het. carrier = possible genotype for children: AA, Aa, Aa, aa (A = normal allele, a = mutant allele). Since this is an infantile form of Tay-sach and he doesn't manifest the phenotype at 30 years old, he does not have it (cross out "aa"). His sibling died from the died from the disease further reinforced the fact that he can only be normal, or het. carrier (AA, Aa, and Aa). So the chance of him being a het carrier is 2/3.

I think there's a rule for it: Within the normal siblings of an affected individual the probability of being a carrier is 2/3.

***Caution, this does not work for all autosomal recessive diesease, especially a late manifesting one.
***Also, in the situation where if the question ask what are the chance of a unborn child in the same family being a heterozyous carrier then it's 1/2 (because in this case you can not eliminate the "aa" genotype)
Excellent explanation! So I think their 3/4 is wrong then!
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  #10  
Old 05-24-2013
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Default 2/3

I would believe that the answer should be 2/3 chance that he is heterozygous.
I feel that brad8930's explanation should suffice , not much to add to it
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