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#1




Why 2 in 3 Probability in this mother?
Husband has cystic fibrosis, mother's sister has cystic fibrosis..chances that child will have the disease? It says 1/3 can someone plz explain the calculation how come mother's probability that she is a carrier is 2/3?
It's a USMLE World Q.. 
#2




probability of passing disease to the child..1/2
probablity of mother being a carrier.2/3..(as one of her sister has the disease and out of the remaining 3 siblings two will be carrier and one will be normal) Chance of child getting the disease..1/2 x 2/3 =1/3 Hope i am correct. 
#3




Quote:
if mother cousin is cystic fibrosis means mothers parents are carrier , from a punnet square taking mothers parents as carrier , propability of mother getting disease is 1/4 [25 percent] but don't have .so mother being carrier according to normal punnet is 2/4, here 4 includes all probabilities, but we already know she is not disease so remove one from 4 ie 3 , so chances of mother being carrier is 2/3 


#4




Quote:
1. Dad is rr 2. Mom is not rr since she does not have the disease. That leaves 3 possibilities: she is RR, Rr, Rr. Note that in 2 out of the 3 remaining possibilities she is a carrier, hence the 2/3. For sure Dad will pass r to the kid, so the kid will either be a carrier or have the disease depending on Mom. If Mom is a carrier, probability she will pass the trait is 1/2. Since 2/3 probability she is a carrier, 2/3 x 1/2 = 1/3 Quote:

The above post was thanked by:  
nevillenic (05032011), tinhi (05172011) 
#5




thank you guys!

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