<prompt> Most common cause of Down syndrome isRobesonian translocationMosaicismMeiotic nondisjuctionEpigenetic mutation  <response>: 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 