Haemophilia A (Factor VIII deficiency)
Haemophilia A is a sex-linked disorder (x-chromosomal recessive). Male dogs express the disease when they have one mutated x-chromosome. The mutated x-chromosome comes from the bitch. In most cases female dogs are carrier of one mutated x-chromosome without being diseased (conductor). According to Mendel's Law of Inheritance, 50% of the male puppies of a carrier bitch will have the mutated x-chromosome and express the disease and 50% of the female puppies will be healthy carriers (conductors). Female dogs will be diseased when they have two mutated x-chromosomes (one from the mother, one from the father). In that case both, father and mother must have the mutated x-chromosome (e.g. diseased male dog bred to conductor bitch).