The X and Y chromosomes are known as the sex chromosomes, all others as autosomes. Genes carried on autosomes can occur it in either sex, but genes carried on the sex chromosomes are transmitted in conjunction with sexual status. A gene carried on a Y chromosome could not appear in a female which only has XX. Few, if any, important genes are carried on the male, largely inert Y chromosome, but a major problem, hemophilia A, is found on the X chromosome. This disease, found in man as well as in the dog, is brought about by the failure of blood to clot or to clot quickly enough. It is the end product of a complex series of reactions, controlled by particular genes or factors. Hemophilia A occurs when factor VIII is impaired. All male offspring obtain their father’s Y chromosome and all get one of their mother’s X chromosomes. If she is a carrier of the defective Xh allele. Male puppies will be hemophiliac and suffer in varying degrees from mild to severe symptoms. Many will die of internal hemorrhaging. All female offspring inherit their father’s normal Xh allele. But while half will get a normal XH from the mother, the other half will inherit the defective Xh and be carriers like their dams. In due course they will transmit hemophilia to their sons even when mated to quite innocent sires. Although sons carry only one Xh, they become hemophiliac because there is no masking XH on the Y chromosomes. Female offspring can theoretically become hemophiliac if a carrier female is mated to an affected male, but as few such males survive to breeding age, and even fewer are bred from, the condition is rarely seen in bitches. Other inherited bleeding diseases are generally autosomal.