Growth occurs through a combination of cell division and cell expansion. Differentiation produces specialized cells and the overall form of the organism is the result of morphogenesis, due to pattern formation. The fate of cells will be determined at different points during development of embryos of different species. In some species, determination occurs relatively early in cleavage, in other, later. Once determination has occurred, the fate of a tissue and its cells are sealed.
Determination precedes differentiation.
The zygote is totipotent and is capable of forming a complete adult. Depending on the species, the cells resulting from cleavage may be totipotent at earlier or later stages in development of the early embryo. Work by several researchers, Briggs and King, Gurdon, and Wilmut demonstrated that differentiation does not involve permanent changes in the genome. Nuclear transplant experiments showed that the nucleus of a differentiated cell could act like the nucleus of a zygote and produce an entire organism. Dolly, the famous cloned sheep is an example of this type of research.