Question

Considering an X-linked dominant trait, if an unaffected woman and an affected man decide to have children, which of the following statements is TRUE about the possibilities for their children?

a. Their sons are expected to be heterozygous for the associated gene.
b.Their daughters are expected to be heterozygous for the associated gene.
c. All their children, whether male or female, are expected to show the dominant trait.
d. All of their sons are expected to show the dominant trait.
e. Their daughters are not expected to show the dominant trait.

Answer 1

Answer: B - Their daughters are expected to be heterozygous for the associated gene.

Explanation: In X - linked dominant trait,

1. Both males and females are affected; often more females than males are affected.

2. Affected fathers will pass the trait on to all their daughters.

3. Affected sons must have an affected mother.

4. Affected daughters must have either an affected mother or an affected father.

5. Affected mothers (if heterozygous) will pass the trait to ½ of their sons and ½ of their daughters.

Check the attached image to see the illustration of how an X - linked trait can be passed from an affected father and unaffected mother to their offspring.