Haemophilia is mentioned as a trait carried by the mother and passed to her sons. What is the pattern of inheritance for this trait?

• A. Haemophilia is an allele carried on one of the mother's autosomal chromosomes.
• B. Haemophilia is an allele carried on the Y chromosome because more males have this genetic disorder than females.
• C. Haemophilia is an allele carried on the X chromosome and can be directly inherited by the son from the father or the mother.
• D. Haemophilia is carried on the X chromosome and can only be inherited by the son if the mother is a carrier.