Fig. 2. Nuclear morphology of 2-cell embryos at the G₂/M border. (A) One cell of a 2-cell embryo in interphase, showing prominent nucleoli (n). Part of the zona pellucida (z) surrounding the embryo is visible on the right. The position of the nuclear membrane is marked by the transition between the clear area surrounding the nucleoli and the more granular cytoplasm. (B) Cell just before nuclear envelope breakdown, exhibiting small, more dispersed nucleoli indicative of prophase. (C) Cell in metaphase, showing absence of nucleus or nucleoli, and an even distribution of granular cytoplasm throughout. Bar, 5 µm.