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  #1  
Old 10-03-2012
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Genetics Tay sachs inheritance

Te parents of girl with Tay- Sachs disease decide to pursue bone marrow transplantation in an attempt to provide a source for the missing lysosomal enzyme. Preliminary testing of the girl's normal siblings is performed to asses their carrier status and their human leukocyte antigen (HLA) locus compatibility with their affected sister. What is the chance that one of the three siblings is homozygous normal (i.e. has a good supply of enzyme) and HLA- compatible?

A. 1/2
B. 1/3
C. 1/4
D. 1/6
E. 1/12

A brief explanation would be nice.
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1/3.........................................
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Old 10-03-2012
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twist is HLA compatible homzygous sibling

may be 1/12

chances of homozygous normal - 1/3
guess 1/4 kid(assuming it to be the affected kid clone ) would be HLA compatible

so 1/3*1/4= 1/12
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Default my answer :)

D. 1/6....
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Old 10-03-2012
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Quote:
Originally Posted by koolkiller88 View Post
Te parents of girl with Tay- Sachs disease decide to pursue bone marrow transplantation in an attempt to provide a source for the missing lysosomal enzyme. Preliminary testing of the girl's normal siblings is performed to asses their carrier status and their human leukocyte antigen (HLA) locus compatibility with their affected sister. What is the chance that one of the three siblings is homozygous normal (i.e. has a good supply of enzyme) and HLA- compatible?

A. 1/2
B. 1/3
C. 1/4
D. 1/6
E. 1/12

A brief explanation would be nice.
My answer E) 1/12.

Chance of being homozygous normal 1/3
Chance of one sibling having the exact HLA haplotype is 1/4.
1/3*1/4=1/12
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I think the answer = the possibility that the sibling is homozygous normal * the possibility that the sibling is hla compatible

tay sachs is autosomal recessive
the possibility that a sibling is homozygous normal is 1/4 because both parents are carrier of tay sachs so their genotype is Aa
so Aa and Aa will give AA, Aa,Aa and aa

So AA which is homozygous normal has a possibility of 1/4

now for hla compatibility I donít know how to calculate it
but after calculating it, it must be multiplied by 1/4 which is the possibility of the homozygous normal

so I will go for e-1/12 assuming that possibility of hla compatibility is 1/3 and multiplied by 1/4 ( the AA possibility ) it is 1/12
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Quote:
Originally Posted by koolkiller88 View Post
Te parents of girl with Tay- Sachs disease decide to pursue bone marrow transplantation in an attempt to provide a source for the missing lysosomal enzyme. Preliminary testing of the girl's normal siblings is performed to asses their carrier status and their human leukocyte antigen (HLA) locus compatibility with their affected sister. What is the chance that one of the three siblings is homozygous normal (i.e. has a good supply of enzyme) and HLA- compatible?

A. 1/2
B. 1/3
C. 1/4
D. 1/6
E. 1/12

A brief explanation would be nice.
E.1/12
Tay-sach's disease being A.R..overall chances of having normal homozygous offspring is 1/4. and they have asked abt chances of being homozygous normal in those 3 siblings=1/3 x 1/4 i.e1/12
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will go with E) 1/12
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Quote:
Originally Posted by Teona View Post
My answer E) 1/12.

Chance of being homozygous normal 1/3
Chance of one sibling having the exact HLA haplotype is 1/4.
1/3*1/4=1/12
Teona why is the chance of being homozygous normal is 1/3 not 1/4? is that because we already know he or she is normal?
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Default errata!

I think I went wrong with my first answer
I think it should be 1/4

1/3 - that the sibling is a homozygous normal
1/4 - that they share the same HLA

so it would be 1/3 x 1/4 = 1/12

the pts has 3 siblings and we don't know for which one we're calculating it so it's equally probable for each sibling to be a homozygous normal and to share the same HLA with the pts. So I think we should multiply that 1/12 by 3 (no. of siblings=no. of possible combinations) = 1/4
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  #11  
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koolkiller88, has Casandra got the correct answer?
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Default Yes casandra- perfect five ;-)

Quote:
Originally Posted by koolkiller88 View Post
Te parents of girl with Tay- Sachs disease decide to pursue bone marrow transplantation in an attempt to provide a source for the missing lysosomal enzyme. Preliminary testing of the girl's normal siblings is performed to asses their carrier status and their human leukocyte antigen (HLA) locus compatibility with their affected sister. What is the chance that one of the three siblings is homozygous normal (i.e. has a good supply of enzyme) and HLA- compatible?

A. 1/2
B. 1/3
C. 1/4
D. 1/6
E. 1/12

A brief explanation would be nice.
possibility that one sibling is homozygous normal- 1/3
Possibility that one sibling is HLA compatible- 1/4

So Chances for a sibling to be homozygous normal for Tay-sachs and HLA compatible- 1/3x 1/4= 1/12

Since 3 siblings so total chances are 1/12x3- 1/4
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Quote:
Originally Posted by taher View Post
Teona why is the chance of being homozygous normal is 1/3 not 1/4? is that because we already know he or she is normal?
Its an AR diz.
So 1/4 will be the probability that one child be homozygous normal but as we know 1 child is already homozygous affect.

So now the probability that one child be homozygous normal would be 1/3
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@koolkiller88- thank you again for that question! it was really nice and tricky!!!

And to all of you guys who posted their answers after me, thank you sooooo much! if it wasn't for you I wouldn't have gone and double checked on this question!
This thread is really terrific!
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Quote:
Originally Posted by koolkiller88 View Post
possibility that one sibling is homozygous normal- 1/3
Possibility that one sibling is HLA compatible- 1/4

So Chances for a sibling to be homozygous normal for Tay-sachs and HLA compatible- 1/3x 1/4= 1/12

Since 3 siblings so total chances are 1/12x3- 1/4
oh! my poorness.......i never understand genetics and ethics problems correctly.......can anyone tell me a good solution for how to get rid of this.........
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Originally Posted by venky2600 View Post
oh! my poorness.......i never understand genetics and ethics problems correctly.......can anyone tell me a good solution for how to get rid of this.........
are you weepingthey will give easy ones in exam
i missed the last part of question but would have bet my last dime its 1/12 ;(
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Quote:
Originally Posted by blade View Post
are you weepingthey will give easy ones in exam
i missed the last part of question but would have bet my last dime its 1/12 ;(
my problem is not with this one problem dude...anyways thanx for ur guidance though
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Old 10-05-2012
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Listening Please clarify more

I didn't get it, why its 1/3 and not 1/4? In other words, I didn't get the idea of that addition ( from 1/4 to 1/3 ). Thank you dude.
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Old 05-25-2013
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So what is the conclusion guys? What's the final answer?
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Old 05-26-2013
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Quote:
Originally Posted by nsesereso View Post
so what is the conclusion guys? What's the final answer?
1/3*1/4=1/12
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  #21  
Old 05-26-2013
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Can u pls tell me from where to read for lysosomal storage disorders...?
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