FloorMatt

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Jul 6, 2015
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Please take a look at this question and explain how a boy can have both hemophilia and color blindness (which are unlinked genes on different x chromosomes). I was under the impression that the boy would get a Y chromosome from the father with no disease... and now the mother passes down one of her X chromosomes to him with EITHER hemophilia or colorblindness. If the mother has one X (hemophilia) and one X (colorblindness) she can only pass down one or the other to this boy? This probability renders to me as 0%. Can someone clarify.

Bootcamp test 2 question...
Screen Shot 2015-08-12 at 7.05.59 PM.png
 

nornton

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Jul 19, 2015
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Not sure, I would have picked 1/4 as well. Hopefully someone can clarify this
 

RenzyBoy

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Aug 12, 2015
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The answer explains it pretty well there, I remember this from bootcamp!

So first, this kind of draws on probabilities in math, you just multiply the individual chances of everything happening.

Since the woman is a carrier for both Hemophilia AND color blindness, the chance of passing along EITHER of them is 1/2. To get both, you multiply the chance of getting hemophilia (1/2) by the chance of getting color blindness (1/2). Now to answer part of your question, it doesn't say that the genes for both diseases are on different chromosomes, so you can't assume that getting one doesn't mean he won't get the other. You don't know which gene is where, and with crossing over and whatnot, it's definitely possible to get both, even if they're on different chromosomes. So you have to work with the probabilities they give you.

Then, from the male side, the chance of the father giving his Y chromosome is ALSO 1/2.

(1/2 chance of getting a boy) * (1/2 chance of getting hemophilia from the mother) * (1/2 chance of getting color blindness from the mother) = 1/8

Hope this helps! :)
 
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510586

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Hey is this reasoning wrong? I did it like pea plants with 2 different traits (kind of like a dihybrid...) but it makes sense since they are on different genes.
 

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RenzyBoy

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Aug 12, 2015
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Hey is this reasoning wrong? I did it like pea plants with 2 different traits (kind of like a dihybrid...) but it makes sense since they are on different genes.
You've got the right idea, but just to prevent yourself from getting confused, rather than two different X chromosomes from the mom, remember that only one get's carried over! So maybe it would be more like Xho, Xoo, Xoc, Xhc, with h being hemophilia, c being colorblindness, and o being nothing. Im not sure if that makes sense typing it out haha
 
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510586

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I think probability is easier to look at not drawn as hybrid. I drew it with two bc it had to be at same time