How are the globin chain genes arranged? Note: a means alpha, B means beta

Correct Answer: B

Rationale: The correct answer is B because the globin chain genes are indeed located on separate chromosomes. The alpha (a) genes are located on one chromosome, while the beta (B) genes are located on a different chromosome. This arrangement allows for independent regulation and expression of the alpha and beta globin chains. Choices A, C, and D are incorrect because they do not accurately reflect the known genetic arrangement of the globin chain genes. Choice A incorrectly states that both a and B genes are on the same chromosome, which is not the case. Choice C is incorrect as it states that there are four a genes and four B genes, which is not accurate. Choice D is incorrect as it states that there are four a genes on one chromosome and two B genes on a different chromosome, which is also inaccurate.

Correct Answer: B

Rationale: The most likely diagnosis is B: Deep vein thrombosis (DVT). In a post-hip replacement patient with painful, pale, and swollen calf, DVT is common due to immobility and hypercoagulability. DVT presents with unilateral swelling, pain, and discoloration. Acute limb ischemia (A) typically presents with sudden severe pain, pallor, pulselessness, and paralysis. Cellulitis (C) presents with redness, warmth, and tenderness, not pallor. Fracture complication (D) would typically present with localized pain and swelling at the fracture site, not in the calf region.

Correct Answer: A

Rationale: The correct answer is A: potentially lethal graft-versus-host disease. Bone marrow transplantation in immunocompromised patients can lead to graft-versus-host disease, where the donor's immune cells attack the recipient's tissues, potentially leading to severe complications or death. This occurs due to the recognition of the recipient's tissues as foreign by the donor's immune system. The other choices are incorrect because B (high risk of T cell leukemia) is not a major problem associated with bone marrow transplantation, C (inability to use a live donor) is not a major problem but a limitation, and D (delayed hypersensitivity) is not a major concern in this context.

Correct Answer: C

Rationale: Neutrophils are attracted to an infected area by phagocytosis of IgE-coated bacteria. This is because IgE antibodies bind to pathogens, activating neutrophils through Fc receptors for phagocytosis. IgM (A) is not directly involved in neutrophil attraction. Vascular permeability (B) is a response to inflammation but does not directly attract neutrophils. Aggregation of C4 and C2 (D) is part of the complement system and does not specifically attract neutrophils.

Correct Answer: A

Rationale: The idiotypic determinants are unique antigenic determinants located within the hypervariable regions of heavy and light chains. These regions are highly variable and contribute to the diversity of antibodies. The correct answer is A because idiotypic determinants are specific to the variable regions of antibodies, not the constant regions. Choices B, C, and D are incorrect because idiotypic determinants are not found in the constant regions or hinge region of antibodies. The variability in the hypervariable regions allows antibodies to recognize and bind to a wide range of antigens, making them crucial for the specificity of the immune response.