Non disjunction :
meiosis 1 : some time homologous chromosomes are failed to separate in meiosis 1 cell division so one cell contain 24 chromosome and another cell contain 22 chromosome
mitosis and meiosis 2 : some time sister chromatids of chromosome are failed to separate in mitotic and meiotic division 2 .
so after mitotic division one cell contain 45 chromosomes and another contain 47 chromosomes. As a result two abnormal somatic cells are developed .In meiosis 2 , one cell contain 22 chromosomes and another cell contain 24 chromosome . As result two abnormal gamete are formed.
