A__ or change in a gene causes the disease hemophilia in 30% of cases of the disease.

Hemophilia A is caused by disruptions or changes (mutations) of the F8 gene located on the X chromosome. Approximately 70% of cases are inherited as an X-linked recessive trait. In the remaining 30%, cases occur spontaneously (i.e. new mutation) without a previously family history of the disorder.

Explanation:

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the correct answer is b