The inheritance of hemophilia. (a) The hereditary pattern of hemophilia in the royal families of Europe reveals that it is a recessive X-linked disease. (b) Because females have two copies of the X chromosome, they can carry one copy of the mutant gene for hemophilia without exhibiting the disease; they have hemophilia only if both X chromosomes carry the mutant gene. Male offspring, having only one X chromosome, are more likely to have the disease; hemophilia occurs about 10,000 times more frequently in males than in females.