Which of the following processes is essential for the development of different cell types in an organism?

Differentiation is the process that enables unspecialized cells to develop into distinct cell types with specific functions. During differentiation, cells undergo changes in gene expression, which leads to the formation of specialized structures and the acquisition of unique characteristics necessary for the functions of various tissues and organs in an organism.

This process is crucial in development as it allows a single fertilized egg to develop into a complex multicellular organism with various cell types, such as muscle cells, nerve cells, and blood cells, each suited to their specific roles. Differentiation is tightly regulated by genetic factors and signaling pathways that ensure the appropriate cells form at the right time and place during development.

In contrast, the other terms do not accurately describe this critical biological process. For instance, while "design" might suggest a plan, it does not represent a biological phenomenon. "Determine" pertains more to decision-making than cellular development, and "dimer" refers to a molecular structure formed by two subunits, which is not related to the process of cell specialization.