Editing Ontogeny (section)

=== Fertilization ===
In humans, the process of [[Prenatal development|fetal development]] starts after [[sperm]] fertilizes an [[Egg cell|egg]] and they fuse together, kickstarting [[Embryo|embryonic development]]. The fusion of egg and sperm into a [[zygote]] changes the surrounding membrane to not allow any more sperm to penetrate the egg, so multiple fertilizations can be prevented. Fusion of a zygote also activates the egg so it can begin undergoing cell division.  Each animal [[species]] might not have specifically a sperm and an egg, but two gametes that contain half of the species' typical genetic material and the membranes of these gametes fuse to start creating an offspring.<ref>{{Cite web |title=fertilization {{!}} Steps, Process, & Facts {{!}} Britannica |url=https://www.britannica.com/science/fertilization-reproduction |access-date=2022-04-08 |website=www.britannica.com |language=en}}</ref>