The fate of a cell can be determined by marking cells of the developing embryo, and observing what they normally develop into, without intervention. With this a fate map of various embryonic regions can be constructed. Cells can be labeled with dyes that fluoresce or alternatively, a cell transplant can be performed where similar cells with different observable features are introduced that allows differentiation in the adult organism. It should be noted however that a particular fate does not imply that a cell could not develop differently if placed in a different environment.
A cell is considered determined when a cell at a particular level of development, if transplanted to a new site, will retain the fate from its original site when transplanted to a new site. This implies a stable change in the internal state of a cell such that its fate is now fixed.
Finally, cell differentiation involves the gradual emergence of cell types that have a clear cut identity in the adult, such as skin, nerve or muscle cells. They are not able to revert and develop into a different cell type. Differentiation involves the expression of so called 'luxury genes'. Genes that are not required for the maintenance of normal cell function, but instead give them characteristics of their particular cell type.
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