in the sex chromosome
which control skin colour
which control the mechanism for blood-clotting
which control the formation of haemoglobin
Explanation
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The correct answer is:
C. which control the mechanism for blood-clotting
Explanation (WAEC/JAMB standard):
Haemophilia is a genetic disorder in which the blood does not clot properly.
It is caused by a mutation in genes that are responsible for producing clotting factors (especially Factor VIII or IX).
Because these genes are faulty, bleeding continues for a long time after injury.
Why the others are wrong:
A. in the s*x chromosome → This is partly true but incomplete. Haemophilia is s*x-linked, but the question asks what the genes control, not where they are found.
B. control skin colour → Unrelated.
D. control haemoglobin formation → That refers to diseases like sickle-cell anaemia, not haemophilia.
Final Answer: C



