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another inheritance question

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theonlytycrane

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https://www.khanacademy.org/test-pr...ice-tut/e/a-family-history-of-marfan-syndrome

Screen Shot 2016-04-28 at 2.57.09 PM.png


Circle = female and square = male. It's not X-linked recessive or mitochondrial.

Any tips on how to decide between autosomal dominant or recessive? A case can be made for both.
 

betterfuture

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Autosomal dominant doesn't skip, autosomal recessive does. Here, every generation is affected. Since both males and females are affected to the same degree, this is not X linked. I am sure you can narrow the choices down to a final answer.
 

bee17

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This isn't a great question, because it technically could be autosomal dominant, autosomal recessive, or x-linked recessive (or even x-linked dominant, although that is not an option). If you get a question like this, try to pick the most likely option without overthinking. The trait shows up in every generation and appears to affect males and females equally, which is characteristic of an autosomal dominant trait.
 
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aalamruad

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https://www.khanacademy.org/test-pr...ice-tut/e/a-family-history-of-marfan-syndrome

View attachment 203019

Circle = female and square = male. It's not X-linked recessive or mitochondrial.

Any tips on how to decide between autosomal dominant or recessive? A case can be made for both.

There's a very important point to recognize when looking at these diagrams: we assume that "outsiders" are NOT carriers. Since 11 is not a carrier (because she is an outsider), but 14 still has marfan syndrome, we know that it must be dominant, because if it was recessive, then 14 and 15 would have to be carriers, and wouldn't express the disease like 14 does in the diagram.
 
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