<prompt> Down syndrome is due to non-disjunction of?21181115  <response>: Ans. is a i.e., 21 Chromosome In 95 of cases of Down syndrome-trisomy of 21:? Extra chromosome is of maternal in origin. 1 have mosaic with some all have 46 chromosome. 4 have robesonian translocation. t 13 21 o t 14 : 21 t 15 : 21 Very rarely long arm of chromosome 21 is triplicate Paial trisomy. 