Final answer:
Cellular commitment and differentiation in multicellular organisms involve selective gene expression directed by transcription factors, resulting in specialized cells from unspecialized stem cells. This process contributes to the complex structure and function of an organism, as seen in the wide array of cells types derived from a single fertilized egg.
Step-by-step explanation:
A cell in a multicellular organism becomes committed to differentiate into a specific cell type during the process of cellular differentiation. This process, which enables a complex organism such as a human to develop from a single cell, the fertilized egg, involves transforming unspecialized stem cells into specialized cells like nerve, muscle, and epithelial cells.
All cells, including the fertilized egg, contain the same DNA; however, through differentiation, cells only express certain genes that are relevant to their unique functions. Transcription factors play a crucial role by promoting or hindering the transcription of genes, leading to the unique genetic expression of each cell type. Once the inner mass of embryonic cells passes the totipotent stage, their developmental paths are determined, and they begin the journey of developing into specialized cell lines.