@sarim/psychmledr/maryam - goal13

[ArchivalUser]

throw some light on the following quetion


http://www.usmleforum.com/showthread.php?tid=685318

[ArchivalUser]

The answer is 1/4

the chance of passing the affected gene from the father to the child is.100% or 1
the chance of mother being carrier is 50% or 1/2
the chance of passing the affected gene to the child from the mother is 50% or 1/2

1*1/2*1/2=1/4

[ArchivalUser]

@ maryam thanks

the carrier rate of mother (whose sibling status not mentioned ) would be 1/2 irrespective of whether both her parients or only one of her parients is a carrier......am i right .

[ArchivalUser]

@maryam i got the chance of mother being carrier is 1/4

pls point out where m i going wrong

should nt we consider
the prob that " mothers" grandparent being a carrier ?so i traced 1 more generation up where theres the disease allele is originally present,assuming they too are normal.
the possible genotypes are AA/Aa or Aa/Aa so risk of allele transfer is 50% whichever is the combo. to the grandmother. so i got 1/8 as answer.

thank you

[ArchivalUser]

@mle2014

Autosomal recessive skips generation:
One generation either normal or carrier
Next generation either carrier or disease

that's why

[ArchivalUser]

As we know the husband suffers from cystic fibrosis(aa) and the wife does not(she could be either a carrier..50%Aa or a healthy..100% AA)
The husband and wife both are cousins,they share one or more common ancestors ,their parents(grandparents of the child),they didn't manifest the disease,but they could be the carriers.

Grandmother(mother of wife) .... Aa
Grandfather(father of wife)..........Aa

The chance of their daugther to be healthy,carrier or sick in order are:

1/4AA......***1/2Aa Carrier***.....1/4aa


The wife does not show any symptoms of disease,but the chance of her to be a carrier is 1/2

Now, we are asked to find the chance of the child to get the disease:

we must calculate the chance of mother(wife)to be a carrier first=1/2 ,then multiply it with the chance of passing of her affected gene to her child=1/2 ,last multiply the result with the chance of passing the father's affected gene=1(he is 100% sick) ...

1/2*1/2*1=1/4

I hope it helps

[ArchivalUser]

Amazing

[ArchivalUser]

thanks a lot maryam i understood my mistake,overthinking did the harm..lol

and thank you so much goal for this "eye opener" Qn.

[ArchivalUser]

You are very welcome

[ArchivalUser]

you are welcome