Answer:
50% or 1/2.
Explanation:
So first off to answer this question, we have to determine the genotypes of the parents first. The key is in the first sentence: Hemophilia is X-linked & recessive. That means two recessive alleles of the trait are needed in order for a person to express its effects and that the trait is specifically found on the X chromosome.
Let's start with the mother. The question states that her father is a hemophiliac. She has to have at least 1 recessive allele for hemophilia then because during sexual intercourse, each parent contributes 1 sex chromosome, and in the case of a daughter, the father must donate an X chromosome. However, the question also states that she is "apparently normal," meaning that the second allele that she has for the disease is not recessive but dominant. Thus we can represent her genotype with "XH Xh."
Let's go onto the father. The father is unaffected, meaning he is neither a hemophiliac nor a carrier. His genotype must be "XH Y". Remember, to be a carrier, he must have 1 recessive allele for the disease, and the Y chromosome cannot carry the allele.
The question asks for "the chance that any of her future sons would be [a] hemophiliac." By now, you should have realized that this would mean the son would have the genotype of "hh." Couple things to note here: 1, the son must get a Y chromosome from his dad and an X from his mom, and 2, we need to use a Punnett square. Let's do the cross.
We get the following: XH XH, XH Xh, XH Y, and Xh Y. However, we need to focus on the sons here, who are represented by XH Y and Xh Y. As you can see, half of them have/express the disease, Xh Y. Thus, the chance that any of her future sons would be hemophiliac is 50%, or 1/2.
Cheers. =-)
