Since the mutations causing the disease are X-linked recessive, a female carrying the defect on one of her X-chromosomes may not be affected by it, as the equivalent dominant allele on her other chromosome should express itself to produce the necessary clotting factors, due to X inactivation. Therefore, heterozygous females are just carriers of this genetic disposition. However, the Y-chromosome in the male has no gene for factors VIII or IX. If the genes responsible for production of factor VIII or factor IX present on a males X-chromosome are deficient there is no equivalent on the Y-chromosome to cancel it out, so the deficient gene is not masked and the disorder will develop.Since a male receives his single X-chromosome from his mother, the son of a healthy female silently carrying the deficient gene will have a 50% chance of inheriting that gene from her and with it the disease; and if his mother is affected with haemophilia, he will have a 100% chance of being a haemophiliac. In contrast, for a female to inherit the disease, she must receive two deficient X-chromosomes, one from her mother and the other from her father (who must therefore be a haemophiliac himself). Hence, haemophilia is expressed far more commonly among males than females, while females, who must have two deficient X-chromosomes in order to have haemophilia, are far more likely to be silent carriers, survive childhood and to submit each of her genetic children to an at least 50% risk of receiving the deficient gene.
A coronary occlusion is the partial or complete obstruction of blood flow in a coronary artery. This condition may cause a heart attack.In some patients coronary occlusion causes only mild pain, tightness or vague discomfort which may be ignored; however, the myocardium, the muscle tissue of the heart, may be damaged. In history
According to Robert K. Massies Nicholas and Alexandra: The Fall of the Romanov Dynasty, Tsar Nicholas II may have suffered a coronary occlusion right before he was toppled from his throne during the Russian Revolution in 1917. See also
Arterial embolism


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