Non disjunction during early embryonic mitotic division of somatic cells in developing zygote. In early embryonic life somatic cells undergo rapid mitotic division. After several rounds of successful mitosis producing normal cells, during subsequent mitosis in one particular cell one copy of a particular chromosome (say chromosome 5) may experience non disjunction leading to the incorporation of both sister chromatids of that chromosome to one daughter cell. If all other 45 chromosomes replicate and segregate successfully, finally in one daughter cell chromosome number will be 47 instead of 46 due to incorporation of both sister chromatids of one copy of chromosome 5 and that in other daughter cell will be 45 due to failure of one sister chromatid of one copy of chromosome 5 to be incorporated in that cell. As a result two types of daughter cells will be generated, one with 47 chromosomes (trisomy 5) and the other with 45 chromosomes (monosomy 5). Subsequently if mitotic divisions proceed even normally without no more non disjunction, then in the same individual three cell lines will develop. One normal cell line with 46 chromosomes, one cell line with 47 chromosomes (trisomy 5) and one cell line with 45 chromosomes (monosomy 5). Ake me understand this