A certain type of very rare deafness in humans is inherited as an X-linked reces

Question

A certain type of very rare deafness in humans is inherited as an X-linked recessive trait. A man who suffers from this type of deafness married a normal woman, and they are expecting a child. They find out that they are distantly related. Part of the family tree is shown below. As a genetic counselor, what would you advise the parents about the probability that the child will be deaf?

An image of the pedigree can be found at the following link (#65)

http://books.google.com/books?id=MsFkrBY2-5AC&pg=PA87&lpg=PA87&dq=a+certain+type+of+very+rare+deafness+in+humans+is+inherited+as+an+X-linked+recessive+trait&source=bl&ots=YPnlK_Dtzv&sig=OTBxzn516ocH9hwG0fjgOF4-8D4&hl=en&ei=aUhYTaqFE4S8lQeyxKCYBw&sa=X&oi=book_result&ct=result&resnum=2&ved=0CBkQ6AEwAQ#v=onepage&q=a%20certain%20type%20of%20very%20rare%20deafness%20in%20humans%20is%20inherited%20as%20an%20X-linked%20recessive%20trait&f=false



Answer

1. 1/128

2. 1/16

3. 1/256

4. the probability is different for a boy and girl

5. 0

6. none of the above



I've been working on this for awhile, and my best answer is 'none of the above'. My reasoning is that the mom could be homozygous dominant or heterozygous for the deaf allele and thus you can't determine exactly what their child would be because you don't know more about the family pedigree, only that the dad is dominant.

Any input would be great, Thank You!

Explanation / Answer

It is given that a rare deafness in humans is inherited as an X-linked recessive trait. So, the boy gets affected if condition is XdY, and girl with both genes-XdXd Man with daefness is married to a normal man, then the progeny are XdY x    XX Progeny - XdX - normal female, carrier XdX - normal female, carrier XY - normal boy XY - normal boy The probability of child getting deaf is 0, as there are no deaf children in the F1 gegeration. But carriers are present, that are responsible for deafness in F2 generation. Man with daefness is married to a normal man, then the progeny are XdY x    XX Progeny - XdX - normal female, carrier XdX - normal female, carrier XY - normal boy XY - normal boy The probability of child getting deaf is 0, as there are no deaf children in the F1 gegeration. But carriers are present, that are responsible for deafness in F2 generation.

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