At which month of fetal development does the bone marrow become the primary site of hematopoiesis?

Correct Answer: C

Rationale: The correct answer is C, the end of the 6th month. By this time, the bone marrow becomes the primary site of hematopoiesis in fetal development. This is because around this stage, the bones have developed enough to support the production of blood cells. Prior to the end of the 6th month, hematopoiesis mainly occurs in the liver and spleen. Choices A, B, and D are incorrect because by the 2nd, 5th, and end of 7th month respectively, the liver and spleen are still the main sites of hematopoiesis in fetal development.

Correct Answer: B

Rationale: The correct answer is B (>95% Hb A, <3.5% Hb A2, <1-2% Hb F). In adults, the normal distribution of hemoglobin includes mainly Hb A (>95%), a small percentage of Hb A2 (<3.5%), and an even smaller percentage of Hb F (<1-2%). This distribution is typical in healthy individuals and represents the normal composition of adult hemoglobin. Choice A (80-90% Hb A, 5-10% Hb A2, 1-5% Hb F) and Choice C (90-95% Hb A, 3-5% Hb A2, 1-3% Hb F) are incorrect because they do not reflect the accurate distribution percentages of Hb A, Hb A2, and Hb F in adults. Choice D (85-90% Hb A, 5-7% H

Correct Answer: B

Rationale: The correct answer is B: Fever. In diagnosing malaria, fever is a key symptom due to the cyclic nature of the disease. Malaria typically presents with recurrent bouts of fever, which is caused by the cycle of the parasite invading and multiplying in red blood cells. The other choices (A: Rash, C: Chest pain, D: Hair loss) are not typical signs of malaria. Rash is more commonly seen in diseases like dengue fever, chest pain could be indicative of other conditions like pneumonia or heart issues, and hair loss is not a characteristic symptom of malaria. Therefore, fever is the most characteristic and essential sign to consider when diagnosing malaria.

Correct Answer: B

Rationale: The correct diagnosis is B: Polycythemia vera. The presence of JAK-2 mutation is a key indicator for polycythemia vera. This condition is characterized by increased red blood cell production, leading to symptoms such as blurred vision, headaches, and splenomegaly. The other choices can be ruled out based on the specific clinical presentation and genetic mutation. Myelofibrosis typically presents with bone marrow fibrosis, not splenomegaly. Essential thrombocythemia is characterized by elevated platelet counts, not red blood cells. Chronic myeloid leukemia typically presents with elevated white blood cell counts and the presence of the Philadelphia chromosome, not JAK-2 mutation.

Correct Answer: C

Rationale: The correct answer is C because genetically identical individuals have the same major histocompatibility complex (MHC) antigens, so there is no immune response or rejection of grafts. Minor histocompatibility antigens (choice A) are not relevant in this case. Hyperacute rejection (choice B) occurs due to pre-existing antibodies, which is not a factor in genetically identical twins. Choice D is incorrect as both kidney and skin grafts would be accepted between identical twins due to genetic similarity.