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Fig. 4922 hours after the fertilization a mitotic spindle has formed (more info).The nucleic membranes of the two pronuclei dissolve. This is the visible sign that the zygote has been created.

Fig. 5023 hours after fertilization: the spindle apparatus in the anaphase; the chromosomes are pushed apart. (More info with videos 620 kB or 940 kB)

The zygote - by definition the first cell of the embryo undergoes only an incomplete cell cycle. With the penetration of the sperm cell, the genetic information of the two parents are not instantly brought together in order that they are then duplicated together and distributed in the subsequent mitosis. In reality, the paternal and also the maternal genetic information are first duplicated in two independent pronuclei and also there condensed again into chromosomes so they can align themselves along the equator of the mitotic spindle.

Link:
The formation of the zygote - Embryology