A woman who is a carrier for a sex-linked recessive trait has children with a man who does not have that trait.
What is true about their offspring?
Choose 1 answer:
Choose 1 answer:
(Choice A) All of their children will be unaffected carriers.
A
All of their children will be unaffected carriers.
(Choice B) They have a
25
%
25%25, percent chance of having an affected son.
B
They have a
25
%
25%25, percent chance of having an affected son.
(Choice C) No son they have would be affected.
C
No son they have would be affected.
(Choice D) They have a
50
%
50%50, percent chance of having an affected daughter.
D
They have a
50
%
50%50, percent chance of having an affected daughter.
The correct answer is:
C) No son they have would be affected.
The correct answer is:
(Choice B) They have a 25% chance of having an affected son.
Explanation:
In this scenario, the woman is a carrier for a sex-linked recessive trait, which means she carries the gene for the trait on one of her X chromosomes but does not have the trait herself. The man does not have the trait.
Since the trait is sex-linked, it is located on the X chromosome. The woman can pass the trait to her children, as she can pass either her X chromosome with the trait or her X chromosome without the trait.
If the couple has a son, he will inherit one X chromosome from his mother and one Y chromosome from his father. If the mother passes on her X chromosome with the trait, the son will be affected by the trait since there is no dominant allele on the Y chromosome to mask the recessive trait. Therefore, there is a 25% chance of having an affected son.
If the couple has a daughter, she will inherit one X chromosome from her mother and one X chromosome from her father. Even if the mother passes on her X chromosome with the trait, the daughter would need to inherit another X chromosome with the trait from her father to be affected. Since the father does not have the trait, the daughter will not be affected.