Further, one percent are of the "mosaicism" type. In this variation, the body simultaneously has cells with 46 chromosomes and others with 47 chromosomes. The cause of this is that at the time the fertilized egg divides, one of the chromosomes doesn't.
此外百分之一屬鑲嵌型，此類型唐氏症患者體內同時含有四十六個染色體及四十七個染色體的細胞，形成原因是受精卵在有絲分裂時發生染色體不分離。