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#1




genetics ques!!
A woman who is a known heterozygous carrier of a PKU mutation marries her half second cousin . What is the probability that this couple will produce a child with PKU??
A.1/16 B.2/9 C.1/64 D.1/256 E.1/128 
#2




Wow half second cousin
Could you please tell where u picked up this Q from? Thanks! 
#3




my answer
I think it's D 1/256 but it's based on many assumptions so really not sure...
my calculations: 1/2 x 1/4 x (1/8 x 1/2 x 1/2) = 1/256 1/2  probability that the husband is a carrier (we have to include that, right??? I mean I assume that he's not affected since the stem doesn't say anything and if he's healthy then they will not have a child with PKU but not sure...) 1/4  probability that, provided both parents are carriers, they will have a child with PKU 1/8  pool of genes their grandaparents shared (half first cousins) x 1/2 x 1/2  portion of genes passed on through 2 generations (from grandparents to the present couple) 
#4




Viral i pick this question from another forum.
Casandra yes i got the same answer when i calculated it 1/32*1/2*1/4 1/32 for second cousins 1/2 for half cousins 1/4 probability of PKU child if both parents are carriers Yes i think we should include the probability of father being a carrier Thanks! 
#5




Quote:
can you explain how and why did you calculate 1/32? thanks 
#6




is D correct?

#7




D is correct
for siblings 1/2 for first cousins 1/8 (1/2*1/2*1/2) for second cousins 1/32 (1/8*1/2*1/2) ans so on... please Correct me if i am wrong regarding half cousin i am not sure i was thinking that we should multiply the whole thing with 1/2.... 
#8




Thanks for the Q or else I would not have known the concept of half cousins!!

#9




What would have been the answer if they were
1. half cousins 2. Second cousins. Thanks 
#10




i dnt get wat u mean by HALF cousins!! cud sm1 explain d relashionship!!

#11




cousin
second cousin1/8x 1/2x 1/2
Husband being carrier 1/2 Affected child of carrier parents 1/4 =1/256
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#12




Quote:
chance that two heterozygotes will produce a homozygous affected child is in1/4 total probability of these events happening together is 1/16x1/4=1/64 please casandra /anyone else correct me as i did a similar question in KLN in population genetics but now i am not getting how the answer turns out to be 1/256 
#13




I agree with offpiste .. That's how I worked it out but half second cousin I dont get
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#14




1/ 32 for second cousin
1/2 for half cousin 1/4 for child being diseased... 1/256 Half first cousins are , cousins who share a single grand parent .. similarly 1/2 second cousins share single great grand parent.... 
#15




Quote:
I didnt understand why you said "Yes i think we should include the probability of father being a carrier" ?? 
#16




Quote:
Do you think we should take probability of husband being carrier as 1/2 ?? The ( 1/8x 1/2x1/2) factor that you have used itself is the probability of husband sharing the same gene as his carrier wife..... Am I wrong ? 
#17




Quote:
.. so the factor 1/16 which u got should be 1/ 64 Hope that helps ,, thanks 
The above post was thanked by:  
offpiste (08262012) 
#18




Quote:
1/2  is a chance of him being a heterozygous carrier of autosomal recessive disease 
The above post was thanked by:  
dr.nitowl (08272012) 
#19




oh ! thanks.. then how can we account for the half cousin thing??

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