Pat of mosaicism 21-trisomy 2121 Oosperm mitosis 2121 12 八 C First generation Disjunction of chromosome 21 during mitosis 2121 2121 212121 21 A八八 seocnd generation Nondisjunction in early cell division of a normal zygotemitosis 21 21 Oosperm 21 21 21 21 First generation 21 21 21 21 21 21 21 21 seocnd generation Disjunction of chromosome 21 during mitosis Pathogenesis of mosaicism 21-trisomy Nondisjunction in early cell division of a normal zygote