[Catalist] Genetics question for Bio/ Human Bio Teachers

[Stephen Zander]

Hi Greg,
Having not seen the full question, in responding to your statement the probability would be 25%.
You must take into consideration the probability of firstly having a daughter (using the genotype provided) and then of a daughter being affected. A punnet square sees 50% probability of a girl of which half have the probability of being affected, so 25%.

Kind Regards

Dr Stephen Zander
Physics Teacher/Noake House Tutor
Phone +61 8 9442 1574
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From: Catalist <catalist-bounces at lists.stawa.net> on behalf of Greg Munyard <gmunyard at kennedy.wa.edu.au>
Reply-To: Catalist <catalist at lists.stawa.net>
Date: Thursday, 26 October 2017 at 9:51 am
To: Catalist <catalist at lists.stawa.net>
Subject: [Catalist] Genetics question for Bio/ Human Bio Teachers

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
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