[Catalist] Genetics question for Bio/ Human Bio Teachers

[Ray Forma]

Greg,

just like physicists saying an astronaut in the International Space station is weightless, human biol teachers are also imprecise in their language when they ask “…will produce an affected daughter?”. In that case what they normally mean is “…produce a child who is a daughter and is affected?”.

In this example, assuming the effect is recessive the probability of being affected is 0.5 (XX – female) X 0.5 (XnXn) = 0.25

If the effect is dominant the probability of being affected also is 0.5 (XX – female) X 0.5 (XnXN) = 0.25

The overall answer is therefore 0.25.

[Why do people look at me strangely when in the evening I sometimes say “Isn’t it beautiful the way we are rolling out of sight of the Sun?”.]

> On 26 Oct 2017, at 09:51, 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%.
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> 
> 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%.
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> Any guidance out there in the ether?
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>  
> 
> Regards
> 
>  
> 
> Greg Munyard
> 
> Senior Teacher – Science
> 
> <image001.jpg>
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> 
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Regards,

Ray Forma
50 Harvest Road, North Fremantle WA 6159, Australia
Tel +61 (0) 428 596 938