A woman who is a carrier for haemophilia marries a haemophilic man. What percentage of their daughters are expected to be affected by the disease?

Step-by-step solution

Haemophilia is an X-linked recessive disorder. The mother is a carrier, so her genotype is X^ H X^ h . The father is haemophilic, so his genotype is X^ h Y . A cross between them ( X^ H X^ h X^ h Y ) produces the following progeny: Daughters: X^ H X^ h (carrier) and X^ h X^ h (haemophilic). Sons: X^ H Y (normal) and X^ h Y (haemophilic). Looking specifically at the daughters, half of them ( 1 out of 2 ) will have the genotype X^ h X^ h . Therefore, 50 % of the daughters are expected to be affected by the disease. A