<P> Some scholars have suggested discontinuing the terms dominant and recessive when referring to X-linked inheritance due to the multiple mechanisms that can result in the expression of X-linked traits in females, which include cell autonomous expression, skewed X-inactivation, clonal expansion, and somatic mosaicism . </P> <P> In humans, generally "men are affected and women are carriers" for two reasons . The first is the simple statistical fact that if the X-chromosomes is a population that carry a particular X-linked mutation at a frequency of' f' (for example, 1%) then that will be the frequency that men are likely to express the mutation (since they have only one X), while women will express it at a frequency of f (for example 1% * 1% = 0.01%) since they have two X's and hence two chances to get the normal allele . Thus, X-linked mutations tend to be rare in women . The second reason for female rarity is that women who express the mutation must have two X chromosomes that carry the trait and they necessarily got one from their father, who would have also expressed the trait because he only had one X chromosome in the first place . If the trait lowers the probability of fathering a child or induces the father to only have children with women who aren't carriers (so as not to create daughters who are carriers rather than expressers and then only if no genetic screening is used) then women become even less likely to express the trait . </P> <P> The most common X-linked recessive disorders are: </P> <Ul> <Li> Red - green color blindness, a very common trait in humans and frequently used to explain X-linked disorders . Between seven and ten percent of men and 0.49% to 1% of women are affected . Its commonness may be explained by its relatively benign nature . It is also known as daltonism . </Li> <Li> Hemophilia A, a blood clotting disorder caused by a mutation of the Factor VIII gene and leading to a deficiency of Factor VIII . It was once thought to be the "royal disease" found in the descendants of Queen Victoria . This is now known to have been Hemophilia B (see below). </Li> <Li> Hemophilia B, also known as Christmas Disease, a blood clotting disorder caused by a mutation of the Factor IX gene and leading to a deficiency of Factor IX . It is rarer than hemophilia A. As noted above, it was common among the descendants of Queen Victoria . </Li> <Li> Duchenne muscular dystrophy, which is associated with mutations in the dystrophin gene . It is characterized by rapid progression of muscle degeneration, eventually leading to loss of skeletal muscle control, respiratory failure, and death . </Li> <Li> Becker's muscular dystrophy, a milder form of Duchenne, which causes slowly progressive muscle weakness of the legs and pelvis . </Li> <Li> X-linked ichthyosis, a form of ichthyosis caused by a hereditary deficiency of the steroid sulfatase (STS) enzyme . It is fairly rare, affecting one in 2,000 to one in 6,000 males . </Li> <Li> X-linked agammaglobulinemia (XLA), which affects the body's ability to fight infection . XLA patients do not generate mature B cells . B cells are part of the immune system and normally manufacture antibodies (also called immunoglobulins) which defends the body from infections (the humoral response). Patients with untreated XLA are prone to develop serious and even fatal infections . </Li> <Li> Glucose - 6 - phosphate dehydrogenase deficiency, which causes nonimmune hemolytic anemia in response to a number of causes, most commonly infection or exposure to certain medications, chemicals, or foods . Commonly known as "favism", as it can be triggered by chemicals existing naturally in broad (or fava) beans . </Li> </Ul>

What disease is caused by a gene on the x chromosome