The best example of epigenetic changes in eukaryote biology is the process of cellular differentiation. During morphogenesis, totipotent stem cells become the various cell lines of the embryo, which in turn become fully differentiated cells. In other words, a single fertilized egg cell – the zygote – divides and develops. The daughter cells change into the many cell types of the mature embryo. These include neurones, muscle cells, epithelium, blood vessels an so on. This happens by activating some genes while inhibiting others.