Question

If a mare is a carrier for an X-linked genetic disease, what percentage of her male foals is expected to be affected with the disease?

A. 0%
B. 25%
C. 50%
D. 100%

Answer 1

Male foals born to a mare that is a carrier for an X-linked genetic disease have a 50% chance of being affected. Females can either be unaffected, carriers, or rarely, affected if they inherit the affected X chromosome from both carrier mother and affected father.

Step-by-step explanation:

If a mare is a carrier for an X-linked genetic disease, male foals (sons) have a 50% chance of being affected with the disease. This is because males have only one X chromosome, which they inherit from their mothers. If the mare is a carrier, her X chromosome may carry the recessive disorder. Males cannot be carriers because they have only one X chromosome, so if they inherit the affected X, they will express the disease.

Female offspring, on the other hand, have two X chromosomes and will only be affected if they inherit the affected X chromosome from both their mother (who is a carrier) and their affected father. If only one of their parents provides the affected X chromosome, they will be carriers like their mother.