Hemophilia A is an X-linked recessive genetic condition. In humans it is due to a mutation in the F8 gene, which encodes a protein called coagulation factor VII. Coagulation factors are proteins important in blood clotting. Individuals with hemophilia, when injured, bleed longer than a normal, healthy individual; the inability to normally clot blood can be life threatening. Hemophilia is much more common in males than in females. Which of the following does NOT explain why this is so?
A. A female with one defective allele makes enough normal coagulation factor VII to clot blood and will not have hemophilia A.
B. Females have to receive a defective allele from both their mother and their father to get hemophilia A.
C. Males are hemizygous for the F8 gene, so they will have hemophilia A if they have one defective allele.
D. Males have to receive a defective allele only from their father to get hemophilia A.
Answer: D
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