Question

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. Males are hemizygous for the F8 gene, so they will have hemophilia A if they have one defective allele
C. Females have to receive a defective allele from both their mother and their father to get hemophilia A
D. Males have to receive a defective allele only form their father to get hemophilia A.

Answer 1

Hemophilia A is more common in males than in females because males have one copy of the F8 gene, while females have two copies. Therefore, females are less likely to have hemophilia A.

Step-by-step explanation:

One reason why hemophilia A is more common in males than in females is because males are hemizygous for the F8 gene, which means they have only one copy of the gene on their X chromosome. If this copy is defective, they will have hemophilia A. On the other hand, females have two X chromosomes, and both copies of the F8 gene would need to be defective for them to have hemophilia A. Therefore, females are less likely to have hemophilia A.

A female with one defective allele can produce enough normal coagulation factor VII to clot blood and will not have hemophilia A. This is why the option A does not explain why hemophilia A is more common in males.

Therefore, option A does not explain why hemophilia A is more common in males than in females.