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: Medicine
True abut 'X' Chromosome inactivation: 
Select and explain. 
A. X gene, B. RNA interference, C. Seen in Male, D. All
A: X gene
Answer: A: X gene 
Explanation: A i.e. X-gene Although females have 2X chromosomes (XX), but due to inactivation (lyonization) genes on one X chromosome becomes transcriptionally inactive. Thus X inactivation prevents expression of most genes on one of the X- chromosome in every cell of femaleQ.