<prompt> The most common chromosomal syndrome is ___Fragile-X-SyndromeTrisomy 18Trisomy 21Trisomy 13  <response>: Trisomy 21 Down;s syndrome is the most common chromosomal syndrome. Chromosomal disorders: These may involve autosomal or sex chromosomes. Involving autosomes Involving sex Chromosomes Down;s syndrome Trisomy 21 Edward syndrome Trisomy 18 Patau syndrome Trisomy 13 Cri du chat syndrome 5p deletion Klinefelter syndrome 47,XXY Turner syndrome 45,XO Ref: Nelson textbook of pediatrics 21st edition Pgno: 659 