Biology Is the Disease in the Pedigree Diagram Inherited in an X-Linked Dominant Manner?

[nokia8650]

I was struggling with interpreting the following pedigree diagram:

http://img245.imageshack.us/img245/715/photoon20100411at2211.jpg

I can see from the diagram that only females seem to be capable of transmitting the disease - not males - this lead me to believe it is X-linked. In addition, I noted that EVERY offspring of an affected female is also affected; leading me to believe it is dominant. This lead to me thinking the condition was inherited in an x-linked dominant manner. However, this would not explain why affected males (who would in my model have the dominant disorder on their X chromosome) do not pass on the condition to their female offspring.

Any help is greatly appreciated.. thanks!

 

[epenguin]

However, this would not explain why affected males (who would in my model have the dominant disorder on their X chromosome) do not pass on the condition to their female offspring.

That appears a conclusive objection!
So you have to consider other possibilities.

 

[nokia8650]

thanks for the reply! I can't really think of anything... would it be possible for you to nudge me in the right direction? Thanks

 

[epenguin]

Just go through X-linked recessive, autosomal dominant and recessive, start with the possible original progenitors' constitution (e.g. original mother must be AA if it is recessive whereas...) write down then the possibilities for F1 etc. and see for each whether there is anything that happens that would be impossible with each starting hypothesis. You cannot offhand predict whether the possibilities are unique or more than one hypothesis is consistent, perhaps someone practiced could see it immediately, not me either.