Early Events
TimeEvent CommentsDrawing
-30sAcrosomeThe sperm acrosome reacts with the egg jelly causing the acrosome reaction.
0BindingThe acrosome reacted sperm binds with the egg. This causes an electrical change in the egg helping prevent other sperm from binding.
30sFusionThe successful sperm's membrane fuses with the egg's plasma membrane
1-2mCortical RxThe cortical granules release causing the fertilization membrane to rise, also helping to prevent further sperm entry.
5mFertilization ConeA cone of actin forms around the sperm nucleus, pulling it into the egg.
10-15mNuclei FuseThe sperm and egg haploid nuclei fuse to become a diploid sea urchin nucleus
20-30mCenteringThe beginnings of the mitotic spindle force the nucleus into the center of the embryo
50-60mStreakThe centrosome replicates causing a spread of microtubules resembling a clear streak.
80-90mMetaphaseThe chromosomes line up in the center of the embryo ready for cell division.
90-120mFirst Division Cytokinesis, cell division occurs. The embryo becomes 2 cells.