This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General pathology, Subject name: Pathology
Most common cause of Down syndrome is 
Select and explain. 
A. Robesonian translocation, B. Mosaicism, C. Meiotic nondisjuction, D. Epigenetic mutation
C: Meiotic nondisjuction
Answer: C: Meiotic nondisjuction 
Explanation: Genetics of Down syndrome 95% cases - Meiotic nondisjunction of chromosome 21 occurring in the ovum 4% cases - Robesonian translocation 1% cases - Mosaicism resulting from mitotic nondisjunction of chr 21