A female child of a mother is diagnosed to have Duchenne's muscular dystrophy. What risk does the mother have for her next male child to suffer from similar illness?
(B) 50% # Duchenne muscular dystrophy is inherited in an X-linked recessive pattern.> Male children, who have an XY chromosome pair, receive one of their mother's two X chromosomes and their father's Y chromo- some. Women DMD carriers who have an abnormal X chromosome have a one-in-two chance of passing that abnormality on to their male children.> Unlike most female children, a male child with an inherited defective Xp21 gene does not have a second X chromosome to provide correct genetic instructions, and the disease manifests.> Sons of carrier females each have a 50% chance of having the disease, and the daughters each have a 50% chance of being carriers.> Daughters of men with Duchenne will always be carriers, since they will inherit an affected X chromosome from their father (note that the diagram only shows the results from an unaffected father).> Some females will also have very mild degrees of muscular dystrophy, and this is known as being a manifesting carrier. In one-third of the cases, the disease is a result of an unspontaneous or new mutation.
25%
50%
100%
0%
Miscellaneous