vanshita wrote:
Tay sachs disease is autosomal recessive disease 50% chance of carrier
25% chance of Normal 25% chance of affected
two sibling already affected chance of carrier 50% divided by 75%
so answer is 2/3 C
ah yeah, that makes more sense, but could you tell me where the 75% came from?
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| vanshita
Forum Guru
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50% + 25% = 75%
because already two sibling affected this person either carrier or Normal
so chances of carrier 50%/75%=2/3
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| equinoxe
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dear vanshita - please explain, I do not understand why do you divide by 75% and where is 75% from? what if there were three or one sibling/s affected?
I would say B is the answer and I would think like this:
1. siblings got the AR disease (they are [aa]), parents have to be carriers [Aa]= heterzygotes
2. 25% healthy (AA)- 50% carrier(Aa) - 25% (aa) diseased and die - since it is an AR disease
i'd say 50% chances of being carrier and it should not matter whether it is one - two - three or four brothers or sisters affected.
do you compute a relative risk versus [un]affected siblings? is this what the q asks?
thank you
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| vanshita
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this pt sibling already affected he has chances either he is carrier or Normal
50% chance of carrier
25% chance of Normal
we want to know what chance of carrier
50%/25%+50%=50%/75%=2/3
25%+50% because he has chances of carrier or Noral genotype
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| mediocre
Forum Elite
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Hi everyone , no offence , but there may be some problem in understanding the word sibling if you think the man hhas to be a carrier....siblings are brothers or sisters not children.
Coming back to the qs,
for the children being affected by a AR ds ,both parents have to be carriers.
so the pedigree and the calculations look likr this(see attachment)
hope this helps,
Attached Files:
AR Carriers.doc (25 KB, 18 downloads)
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| rubina
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QUESTION IS ASKING ABOUT MAN HIMSELF NOT ABT SIBLINGS.SO MAN(FATHER) WILL DEFINITELY BE A CARRIER I00 PERCENT.I THINK ANSWER OPTIONS R NOT RIGHT.
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| mediocre
Forum Elite
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hi,rubina ,thats what I thought in the beginning but infact there is nothing in the question which states that the man IS the father....isint it,so the only way out is His siblings are mentioned and He himself is normal and so wats the risk of his being a carrier....
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