[Catalist] Genetics question for Bio/ Human Bio Teachers

[Lauren Clarke]

Hi Greg, 

In my experience the question has already specified that it’s asking about a girl, so you remove the chances of boys and then you look at the resulting genotypes of the girls so I agree should be 50%

Lauren Pascoe
Sent from my iPhone

> On 26 Oct 2017, at 9:51 am, Greg Munyard <gmunyard at kennedy.wa.edu.au> wrote:
> 
> Good morning folks
>  
> My colleagues and I are having some discussion around this question and I wondered if there is a consensus in the Bio/ Human Bio community on this:
>  
> “If II-8 (XnY) and II-9 (XNXn) have more children, what is the probability that they will produce an affected daughter?” (Genotypes not in the original question – had to be ascertained from a pedigree.)
>  
> One colleague’s approach is to say that there is a 50% chance for producing a daughter and 50% chance that a daughter will be affected so the combination of these is a probability of 25%.
>  
> My approach is to say that there is zero chance for sons to be daughters so that they represent a null sample. Considering only daughters then the chance of an affected daughter is 50%.
>  
> Any guidance out there in the ether?
>  
> Regards
>  
> Greg Munyard
> Senior Teacher – Science
> <image001.jpg>
>  
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