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 Once upon a time.......  

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Bob,a carpenter, suffered from a rare XR ds ,he had a daughter who got married and had a teenage daughter and a son who has the same ds as his grandpa,Bobs grand-daughter gives birth to a normal healthy boy but after an advice from one of her friends is worried about her second issue and meets a famous human genetist and tells him about his brother and grandpa, and that she is planning to have a second child ,and is apprehensive if his second child would be as normal as the second one. She asks the Doctor if she is a CARRIER of the ds .Considering you are the doctor what would be the right statement

1.yes,she is a carrier
2.relative probability of her being a arrier is 2/3.
3. there is 50% chance of her being a carier
4. relative probab of her being a carrier is 1/3


shaking head


He has 50% risk to be a carrier. His mother is a carrier ( has the X with the disease from Bob and she transmited the disease to her son) and the risk to transmit to her daughter is 1/2 ( because the daughter receives one X from her father and one X from her mother but you dont't know what X is tranmited) .


sorry- was "She has"...


This is an application Baye's Theorem, which basically means that since she already has a healthy son...her chances of being a carrier a slightly reduced.

It's hard to 'type out' Baye's theorem, as there's calculation involved, but the answer is 1/3.

(You can find it in genetics books)


sorry,try again.(the probability after a normal child changes,yes-before the birth of a normal son it was 50%)


oops !the above thread was reply to blueocan,.....


young doc nod




oops i misunderstood the Q...somebody pls explain hw cud it be? answer is supposed to be 50 % right?


hERE YOU GO.....


Attached Files:
Her first child is a boy and he is affected.doc (37 KB, 18 downloads)


Great post Mediocre. Or you can simply use my shortcut and do:

1 / [(2^x) +1]

Where x is the number of healthy sons. I derived this 'formula' during my genetics class in med school!

In this case she has one healthy son, so:

1 / [(2^1) + 1] = 1/3


Thank you, guys!
Mediocre , please, can you post the attachment one more time because I can not open it!


thanks young doc or rather young scientist!!!wink

try this blue ocean.....

Attached Files:
Her first child is a boy and he is affected.doc (37 KB, 19 downloads)

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