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: Gynaecology & Obstetrics
[{'content': 'One of the following forms the basis for chromatin testing? \nSelect and explain. \nA. Barr body, B. Testosterone receptors, C. Hormone levels, D. Phenotypic features', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. a. Barr body', 'role': 'assistant'}]