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  #1  
Old 11-28-2012
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Genetics Hardy Weinberg Genetics

Clearly I fell asleep in genetics when we learned this. now its coming back to haunt me. IM lost and would like someone to teach me how to solve questions like these. PLEASE


In a small city with a stable Caucasian population, the carrier frequency of cystic fibrosis is 1/30. In a nearby community, the cystic fibrosis carrier frequency in Asians is 1/100. What is the probability that a child born to a mother from the Caucasian community and a father from the Asian community will suffer from the disease?
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Old 11-28-2012
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For probability questions you have to multiply....
Since cystic fibrosis is an Autosomal Recessive condition, both parents must carry the allele to pass it on to the next generation.
If either parent is a carrier, the probability that the child will inherit the mutant allele is 1/2.
So

Mother= 1/2 * 1/30 Father= 1/100 * 1/2
1/60 * 1/200

answer: 1/12000
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Old 04-04-2013
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Mmm.. doesn't this answer only assume if the parents were only carriers? Don't we have to account for if the homozygous recessive parents were to meet?

ie.
Carrier = 1/30 = 2pq
Homozyg Recess = 1/60

Then you have to calculate total probability of a Carrier from the caucasian community, with a carrier from asian, or with a homozygous recessive from asian, and vv?

I feel like we completely ignored the homozygous recessive.

Can someone double check me?
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Old 04-04-2013
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chances of mother being carrier = 1/ 30
chances of father being carrrier =1/100
chances of 2 carrier mating n produciing affected child = 1/4
therefore chances of child being affected is = 1/4* 1/30* 1/100 = 1/12000
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Old 04-05-2013
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Again... what about the homozygous recessive? Is this kind of a question assuming that both of the parents are only carriers, and can't be homozygous recessive?

Carrier frequency is only telling us 2pq (heterozygous) and nothing about q2 isn't it?

Thanks!
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Old 04-05-2013
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Quote:
Originally Posted by Jun1023 View Post
Again... what about the homozygous recessive? Is this kind of a question assuming that both of the parents are only carriers, and can't be homozygous recessive?

Carrier frequency is only telling us 2pq (heterozygous) and nothing about q2 isn't it?

Thanks!
If they are homozygous recessive,then they clearly mention thier phenotype(affected with CF)..In the above question,they didnt mention any such,so we hav to consider they are phenotypically normal(can be homozygous for normal allele or heterozygous for mutant alelle ). Thus u calculate carriers who appear phenotypically normal and their chance of producing affected child.
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Old 04-05-2013
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Quote:
Originally Posted by Jun1023 View Post
Again... what about the homozygous recessive? Is this kind of a question assuming that both of the parents are only carriers, and can't be homozygous recessive?

Carrier frequency is only telling us 2pq (heterozygous) and nothing about q2 isn't it?

Thanks!
question is about carriers or 2pq
that is why u multiply the carrier frequency by 1/2=chance of carrier mom or dad giving affected gene

if it was q2 or (disease frequency)-than there would be no need for multiplication by 1/2
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