Which of the following is an example of an X-linked recessive disorder? MCQ with Answer and Explanation

Which of the following is an example of an X-linked recessive disorder?
A. Hemophilia
B. Sickle cell anemia
C. Down syndrome
D. Cystic fibrosis
Answer: Option A
Solution (By JKExamLibrary)
Hemophilia A and B are X-linked recessive disorders caused by mutations in genes for clotting factor VIII or IX on the X chromosome. It predominantly affects males, while females are usually carriers. Down syndrome is an autosomal aneuploidy, cystic fibrosis and sickle cell anemia are autosomal recessive. X-linked disorders follow a characteristic pattern of inheritance.

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The hormone that stimulates the kidney to convert 25-hydroxyvitamin D to active 1,25-dihydroxyvitamin D is:
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B. Calcitonin
C. PTH
D. ACTH

Correct Answer: Option C


Explanation:
Parathyroid hormone (PTH) activates the enzyme 1-α-hydroxylase in the kidney, converting vitamin D to its active form, which then increases calcium absorption.

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Question #2
The part of the brain that coordinates voluntary muscle movements and maintains balance is the:
A. Cerebellum
B. Thalamus
C. Cerebrum
D. Medulla oblongata

Correct Answer: Option A


Explanation:
The cerebellum, located at the back of the brain, integrates sensory input and fine-tunes motor activity, posture, and equilibrium. The cerebrum handles conscious thought and voluntary actions, the thalamus relays sensory information, the medulla controls vital autonomic functions like breathing and heart rate.

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Which enzyme catalyzes the primary carboxylation reaction in the Calvin cycle?
A. Nitrogenase
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Correct Answer: Option B


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