genetics question

[destroythemcat]

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Q: When 2 people are carriers for a genetic defect that is autosomal recessive and they subsequently have four children. How many of their children will hypothetically inherit the genetic defect?

A: 1/4

--> why is the answer not 1?…..if each child has a 1/4 of a chance of getting the disease and they have 4 children would we not add add 1/4+1/4+1/4+1/4?

 

[destroythemcat]

But the question asks how many of there children will carry the disease--->isnt the answer 1 child will carry the disease and not 1/4 of a child will carry the disease????

 

[DrknoSDN]

Just a poorly worded question. It's not saying they have a quarter of a child with the disease. It's that 1 of 4 children will have it.

They were running out of printer ink and wanted to save space.

 

[destroythemcat]

Im not sure....i think that each child's chance of getting the disease is the same as if they only had one child....so each child still only hase 1/4 of having the disease

 

[DrknoSDN]

Q: When 2 people are carriers for a genetic defect that is autosomal recessive and they subsequently have four children. How many of their children will hypothetically inherit the genetic defect?
A: 1/4
--> why is the answer not 1?…..if each child has a 1/4 of a chance of getting the disease and they have 4 children would we not add add 1/4+1/4+1/4+1/4?

What is the source of this question? Review book or web based? What were the other 3 choices?

I'm curious what company would be so careless to answer a clearly integer required question ("how many children...?") with a non integer answer.
The question is specifically asking for the number of children, it doesn't say anything about ratio, fractions, or odds. So the answer should be 1. I'm guessing the other 3 answer choices were just more incorrect.

 

[Chrisz]

Based on the question, if they have 4 children, the expected # of children would be 1. It is a simple binomial probability in stats. This question is essentially errored. the probability of passing on the genetic defect (phenotypically) is 1/4. so the prob of not passing on is 3/4. The expected value # of children in 4 is simply 4(1/4)=1.