Question

Hemophilia is caused by an X-linked recessive mutation in humans. If a woman whose paternal uncle (fathers brother) was a hemophiliac marries a man whose brother is also a hemophillac, what is the probability of their first child having hemophilia (Note: assume that there are no other cases of hemophila in the pedigree and no hidden carriers)? Select one: O a. 1/2 O b. 1/8 O c.0 O d. 1/4 O e. 1

Answer 1

Answer:

c. 0

Explanation:

The probability of their first child having hemophilia is 0.

Since hemophilia is is an X-linked and recessive, a man will either be affected or not affected while a woman can be affected, unaffected or be a carrier of the disease.

If the paternal uncle (not the father) of a woman is hemophilic and there is no history of the disorder in the woman's mother's family, such woman is unaffected for the disorder. Hence, her genotype will be $X^HX^H$ (assumming the allele for hemophilia is represented by h).

A man whose brother is hemophilic without himself being hemophilic will have the genotype $X^HY$.

Crossin the two in marriage:

$X^HY$   x   $X^HX^H$

progeny: $X^HX^H, X^HY, X^HX^H, and X^HY$

None of the progeny will have hemophilia.

Hence, the probability of their first child having hemophilia is 0.

The correct option is c.

Answer 2

Answer:

c.0

Explanation:

Given, that apart from woman's paternal uncle and man's brother there are no more haemophilia cases and carriers in pedigree. This means that the woman's parents are not carrying the haemophilia allele and hence she will be non haemophiliac and non carrier. The man's parents are also not carrying the allele hence he will be non haemophiliac. Both man and woman are not carrying any allele for haemophilia so when they have children the probability of having haemophiliac children will be 0.

Hence, the probability of their first child having haemophilia will be 0.