3.2 Understand that fertilisation involves the fusion of a male and female gamete to produce a zygote that undergoes cell division and develops into an embryo

Fertilisation involves the fusion of a male and female gamete. In mammals, this is the sperm (male) and egg (female). This produces a zygote, which undergoes division by mitosis (so all the cells produced are identical) and eventually develops into an embryo.

At this stage, the cells are unspecialised. They later develop into more specific cells (i.e skin, muscle, brain, blood, etc)