This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fertilization and Development of Embryo, Subject name: Anatomy
[{'content': 'Primitive streak is initiated and maintained by \nSelect and explain. \nA. Nodal gene, B. BMP4, C. FGF, D. Brachyury gene', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. is \'a\' i.e. Nodal gene "The primitive streak in itself is initiated and maintained by expression of Nodal, a member of the transforming growth factor b (TGFb) family." - Longman\'s Medical embryology 10/e, p 57', 'role': 'assistant'}]