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
One of the following forms the basis for chromatin testing? 
Select and explain. 
A. Barr body, B. Testosterone receptors, C. Hormone levels, D. Phenotypic features
A: Barr body
Answer: A: Barr body 
Explanation: Ans. a. Barr body