Aneuploidy(非整倍性) Trisomy(三体): three copies 47XY+2 1: Down syndrome Monosomy(单体): one copy 45, X: Turner syndrome Nondisjunction(不分离): failure of a pair of chromosomes to separate(to disjoin) normally in meiosis I or IlAneuploidy（非整倍性） • Trisomy（三体）: three copies – 47,XY+21: Down syndrome • Monosomy （单体） : one copy – 45,X: Turner syndrome • Nondisjunction（不分离）: failure of a pair of chromosomes to separate (to disjoin) normally in meiosis I or II