Question

A woman and man have approached you for genetic counseling and are concerned about a hereditary form of deafness in their family. Both have normal hearing and there are no children. The woman's father has autosomal dominant sensory-neural deafness. Assume he is heterozygous. This hearing impairment displays onset at about age 10, and penetrance appears to be about 70%. There is no family history of deafness among the man's relatives. What is the probability that the woman is a carrier of the deafness allele?

3/10

0

3/13

3/20

1/2

that's all the information I have

Answer 1

Answer: zero ( 0 ).

Reason:

From the question, we know that the trait is autosomal and not x linked and therefore the woman need not suspect if she is a carrier. Also, the woman has normal hearing and if she did carry the dominant gene, the disease would have expressed in her at the age of 10.

Hence we can infer that she does not carry the gene for deafness and that her genotype is dd which means she has zero probability of transfering a defective gene in to the next generation.

.

Let us denote the allele for dominant autosomal sensory neural deafness as D

and the recessive allele for the normal trait is denoted as d.

Genotype of the woman's parents > Male X Female

Dd dd

Gametes > D , d d

F1 > Dd (has the disease) , dd (normal condition)

dd (woman) X dd (husband)

F2 > dd (normal hearing)