|The sperm acrosome reacts with the egg jelly causing the acrosome reaction.
|The acrosome reacted sperm binds with the egg. This causes an electrical change in the egg helping prevent other sperm from binding.
|The successful sperm's membrane fuses with the egg's plasma membrane
|The cortical granules release causing the fertilization membrane to rise, also helping to prevent further sperm entry.
|A cone of actin forms around the sperm nucleus, pulling it into the egg.
|The sperm and egg haploid nuclei fuse to become a diploid sea urchin nucleus
|The beginnings of the mitotic spindle force the nucleus into the center of the embryo
|The centrosome replicates causing a spread of microtubules resembling a clear streak.
|The chromosomes line up in the center of the embryo ready for cell division.
|Cytokinesis, cell division occurs. The embryo becomes 2 cells.