Fig. 2.

The molecular biological mechanisms that mosaicism is more common in early cleavage-stage embryos. a The shift from meiotic toward mitotic mode of spindle might disturb the stability of genome. b The diminished maternal transcripts before the activation of the embryo genome at the 8-cell stage and the increased self-sufficiency after the activation of the human genome. c The spindle assembly checkpoint (SAC) could not effectively inhibit anaphase-promoting complex/cyclosome (APC/C) activity in early embryos and would strengthen as cell size decreases progressively. The Polo-like kinase 1 (PLK1) and BUB-1 show compromised level before the activation of the embryo genome at the 8-cell stage compared with the subsequent blastocyst stage. Cell cycle controls remain at a low-level until 8-cell stage and increase in later stage. d There is overexpression of cell cycle drivers, and in the blastocyst, the opposite is true