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Autosomal or X-Linked?

Genetics as it applies to evolution, molecular biology, and medical aspects.

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Autosomal or X-Linked?

Postby smirnoff » Fri Oct 29, 2010 10:21 am

Hi,

I'm having difficulty telling the the difference between autosomal (dominant and recessive) and x-linked inheritance patterns. I've got to learn it for BMAT but it always seems to me that there's not enough info in the questions to tell the difference...

Eg) Examine the pedigree below of a genetic disorder [affected male has kids with unaffected female]. 3 of their children are unaffected, one female is affected.

Would I be correct in saying the inheritance pattern is autosomal recessive? Just for the male to be affected he'd have to be rr (and the female then Rr) - but this would give two affected children... :?
Or is it an autosomal dominant inheritance pattern where the male is Rr and the female rr?

The rule I've been going by is if there is 1/4 affected offspring its a recessive allele causing the disorder. If there are two or more/4 affected offspring then its a dominant allele causing the disorder. Is this correct in all cases (if any)?! And how do you then tell if it's an x-linked disorder instead of an autosomal one?


Hope some of that makes sense :?

Cheers
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Postby JackBean » Fri Oct 29, 2010 12:31 pm

Your example cannot be autosomal reccesive, because all the kids had to be ill then.

The X/Y-linkage you can decide based on male/female illness. E.g. if in your example they have also unaffected female, it cannot be X-linked, because all female offspring had to be affected (the father has only one bad allele, which must get all daugthers). On the other hand, if only men were affected, it could be Y-linked
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Re: Autosomal or X-Linked?

Postby smirnoff » Fri Oct 29, 2010 3:05 pm

That's what I thought, but the answer guide gave it as an autosomal recessive disorder... :?

Reassuring to know that I don't have it completely wrong then :)

Thanks
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Postby JackBean » Fri Oct 29, 2010 8:28 pm

sorry, my bad, it can be recessive in your example, I was thinking about the X-linked version... :(
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