This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genetics And Genetic Disorders, Subject name: Pediatrics
Chromosome involved in Down's Syndrome is - 
Select and explain. 
A. 21, B. 22, C. 13, D. X chromosome
A: 21
Answer: A: 21 
Explanation: Ans. is 'a' i.e., 21 o Has been explained in previous sessions