Down's syndrome is most commonly caused by ?
Ans. is. 'a' i.e., Maternal nondisjunction o The most common cause of trisomy 21 (Down's syndrome) is maternal nondisjunction in meiosis 1. In most cases the meiotic nondisjunction of chromosome 21 occurs in the ovum and in 95% of the cases the extra chromosome is of maternal origin.
Maternal nondisjunction
Paternal nondisjunction
Translocation
Mosaicism