QuestionSBA
QuestionChoice
The father is unaffected therefore his X chromosome has the dominant allele.

This confirms that if they had a girl she may be a carrier but would not be affected by this condition
10005869
d
100%
QuestionChoice
Haemophilia is an example of an X-linked recessive condition. This means the gene is only carried on the X chromosome; females inherit 2 copies and males only inherit 1. Therefore, males only need to inherit 1 copy to have the disease and females need 2 copies.

As the father is unaffected and does not carry the gene, the X chromosome will have the dominant allele. Therefore, if the couple has a girl they will not have the disease but there is a 50% that they will be a carrier.

There is a 50% chance of having a boy and a 50% chance of a mother passing on her X chromosome with the recessive gene, therefore the overall risk is 25%.
10005866
a
25%
QuestionChoice
If they had a boy, there would be a 50% chance this child would inherit the allele from the mother and have the disease.

However, this question is asking about the risk overall not based on the sex of the baby.
10005867
b
50%
QuestionChoice
There is a 75% chance the child would NOT have the condition.
10005870
e
75%
QuestionChoice
There is a 50% chance the mother will pass on this gene. Therefore, the case of a child being affected by the condition is above 0%.
10005868
c
0%
Concept
Chapter
2693
4453
X-linked Recessive conditions
Topic
205
Genetics
13720
A heterosexual couple attends a fertility clinic to discuss their options for conception.

Mother is a known carrier of haemophilia.
Father is unaffected.

What is the likelihood the child will have the disease?
a