<prompt> Downs syndrome is most commonly caused by:Maternal NondisjunctionPaternal NondisjunctionTranslocationMosaicism  <response>: Most common cause of Down syndrome trisomy is meiotic nondisjunction. Since maternal age is a significant factor for the incidence of Downs, it also suggests that in most cases the nondisjunction takes place in the ovum Maternal Nondisjunction. Ref: Robbins Basic Pathology, 7th Edition, Page 230; Essentials of Human Disease By Leonard Crowley, Page 112. 