Table 1. Comparison of timings in human and mouse preimplantation development.

	Human	Mouse
First cleavage division	27 to 30 hpf (Mio and Maeda, 2008; Wong et al., 2010; Kirkegaard et al., 2012)	16 to 20 hpf (Arav et al., 2008; Kirkegaard et al., 2012)
Blastocyst implantation	6 to 8 dpf (Hertig et al., 1956)	4 to 4.5 dpf (Finn and McLaren, 1967)
Totipotent embryo	Up to four-cell (Van de Velde et al., 2008)	Up to two-cell (Tarkowski, 1959; Rossant, 1976)
Major ZGA	Four- to eight-cell (Tesarík et al., 1987; Braude et al., 1988; Dobson et al., 2004; Vassena et al., 2011; Yan et al., 2013)	Two-cell (Flach et al., 1982; Aoki et al., 1997; Hamatani et al., 2004)
DNA demethylation	Before two-cell (Guo et al., 2014b)	In early one-cell (Mayer et al., 2000; Oswald et al., 2000)
Chromatin accessibility	Increases during cleavage stages; detectable promoter accessibility correlates with timing of ZGA (Gao et al., 2018; Li et al., 2018)	Increases during cleavage stages; detectable promoter accessibility correlates with timing of ZGA (Lu et al., 2016; Wu et al., 2016)
Higher-order chromatin structure	No data available	Gradual establishment during cleavage stages (Du et al., 2017; Flyamer et al., 2017; Gassler et al., 2017; Ke et al., 2017)

dpf, days post-fertilization; hpf, hours post-fertilization.