In Duchenne muscular dystrophy (X-linked recessive), the mother is a carrier and the father is unaffected. What percentage of their daughters will be carriers?

The carrier mother is heterozygous (Xx); the unaffected father contributes a normal X to all daughters. Each daughter has a 50% chance of inheriting the affected X from her carrier mother (making her a carrier, Xx) and a 50% chance of inheriting the normal X (making her unaffected, XX) — so 50% of daughters are expected to be carriers.