The developmental potential , or potency, of a cell describes the range of different cell types it CAN become. The zygote and its very early descendents are totipotent - these cells have the potential to develop into a complete organism. Totipotency is common in plants, but is uncommon in animals after the 2-4 cell stage. As development proceeds, the developmental potential of individual cells decreases until their fate is determined. Determination implies a stable change - the fate of determined cells does not change.
Differentiation follows determination, as the cell elaborates a cell-specific developmental program.
Differentiation results in the presence of cell types that have clear-cut identities, such as muscle cells, nerve cells, and skin cells. The specific components of a given cell provides its special characteristics. These components are either synthesized by proteins, or are themselves proteins. However, the Northern blots shows that only tissue A contains RNA transcribed from that particular gene. Differential gene expression is not a result of differential loss of the genetic material , DNA, except in the case of the immune system.