Final answer:
During early embryonic development, the process through which cells specialize is known as differentiation. Stem cells, which are undifferentiated, have the capacity to become specialized cells, and unique genetic expression occurs as specific genes are turned on or off by transcription factors.
Step-by-step explanation:
During early development, the cells in the embryo of a multicellular organism become specialized through a process called differentiation. This is how a complex organism, such as a human, develops from a single cell, a fertilized egg, into the vast array of cell types that characterize the adult, including nerve cells, muscle cells, and epithelial cells. Stem cells are undifferentiated cells that have the potential to divide and differentiate into specialized cells, which form unique structures and functions as the organism develops.
Each cell begins with the same DNA, but as differentiation occurs, specific genes are expressed while others are not, leading to a unique genetic expression for every cell type. This process is analogous to actors in a movie reading from the same script but only performing their individual parts. The transcription factors play a significant role in determining which genes are turned on or off, thus guiding cells into their specialized forms.