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An X-linked genetic disease is one that is generally passed on from mother to son. The genetic abnormality is found on the X chromosome. Males have the sex chromosome make-up of XY. Males inherit the X chromosome from their mother and the Y chromosome from their father. Since this is the case, abnormalities on the X chromosome from the mother will usually manifest as a disease within 50% of her sons. Although rarely seen in girls and women, these diseases can affect them as well. Since females have a chromosomal make-up of XX, inheriting an X chromosome with disease mutations in it generally will not produce the disease condition. The healthy X chromosome that the female has inherited from her other parent masks the diseased X chromosome. The female with one mutated X chromosome would be known as a carrier because she can pass the mutation onto her children, though she may not be directly affected by it. An X-linked disease could affect a female if her mother is a carrier and the disease affects her father. If her mother and her father are both affected with the disease, she will most certainly be afflicted with the disease as well. In addition, some X-linked conditions produce mild symptoms in women that are carriers.
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The above pictures show the sex chromosome make-up of males and
females. The pictures were created in MS Paint v98 by the Microsoft
Corporation.
Click on one of the pictures to see an animation of the way sex chromosomes are passed from parent to child. |
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