This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pediatrics
[{'content': 'The primary defect which leads to sickle cell anemia is – \nSelect and explain. \nA. An abnormality in porphyrin part of hemoglobin, B. Replacement of glutamate by valine in β–chain of HbA, C. A nonsence mutation in the β chain of HbA, D. Substitution of valine by glutamate in the a–chain of HbA', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Sickle cell anemia\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\n\nSickle cell anemia is a hereditary hemoglobinopathy, i.e. the type of disease characterized by the production of defective hemoglobin.\n\nNormal hemoglobin\n\nThe hemoglobin molecule is an assembly of four globular protein.\nEach subunit is composed of a protein part, i.e, globin and a nonprotein part, i.e. heme, i.e. Each hemoglobin molecule contain four heme units and two pairs of a similar protein, globin.\nThe heme part of the globular protein is same in all types of hemoglobin.\nThe protein part vary in different hemoglobin -\n\n\nAdult hemoglobin (Hemoglobin A) consists of two identical α-chains and two identical δ-chains.\nFetal hemoglobin (HbF) consists of two identical a-chains and two identical γ chains.\nMinor hemoglobin (HbA,) consists of two identical a-chains and two identical δ chains.\n\n\nNormally adult blood contains about 96% of HbA (α2 β2) 3-3.5% HbA2(α2 δ2), and small amount of fetal hemoglobin HbF (α2\xa0γ2).\n\nDefect in sickle cell anemia \n\nSickle cell anemia results from a mutation in β-globin gene.\nIt is caused by a point mutation at the sixth position of the β-globin chain leading to a substation of a valine residue for a glutamic acid residue. resulting in sickle hemoglobin (HbS).\nSickle cell anemia is an autosomal recessive disorder.\nIf an individual is homozygous for the sickle cell mutation, almost all the hemoglobin in the red cell is HbS.\nIn heterozygotes, only about 40% of the hemoglobin is HbS, the remainder being normal hemoglobins.', 'role': 'assistant'}]