When exactly do gamete nuclei fuse?

I'm a bit confused, its says that when the sperm and egg fuse to form a zygote. But then they add that the 2 nuclei don't fuse immediately instead the cell divides by mitosis to begin zygote formation. What gives?

The two pro-nuclei don't really fuse as such - they just enter mitosis together.

The cytoplasm etc fuses, so the initial zygote will have two pro-nuclei.

All right, out of curiosity when does it happen then?

Well roughly:

- sperm and oocyte fuse to form a zygote with two pro-nuclei
- DNA replication in each pro-nuclei
- Each pro-nuclei undergoes prophase separately
- The nuclear envelopes then disappear and all the chromosomes from both male and female pro-nuclei line up on the metaphse plate
- Rest of mitosis as normal