Human preimplantation embryos have a high incidence of aneuploidy. The occurrence of aneuploidy looks starts during meiosis continuing till day 3 of embryonic development (meiotic and mitotic errors). After day 3, embryonic genome activity is gradually activated and cell cleavage checkpoints (CCC) gradually matures and functions. In normal situation, the CCC eradicates of aneuploid blastomeres through arrest and apoptosis. At day 3, the aneuploid incidence of each chromosome is similar about 20-30% while at blastocyst stage the aneuploid incidence of each chromosome varies from 2-10%. The aneuploid rate of examined chromosomes is significant different between the examined stage (p <0.0001). The aneuploid incidence is significantly reduced with development. The reduction of aneuploid incidence is different among chromosomes. The reduction efficiency appears related to the chromosomal gene content and/or genes involving with CCC or apoptosis. Chromosomal aneuploid reduction incidence is related to gene content, high gene content is purged earlier, i.e. chromosome 1 and 19, while low gene content is purged late, i.e. chromosome 13, 21, 22.