What is the term for the process by which cells become specialized through selective gene expression?

The correct answer is differentiation. This term refers to the process through which cells undergo a series of changes that lead them to become specialized in structure and function. During differentiation, specific genes are expressed while others are suppressed, enabling a cell to acquire distinct characteristics that are necessary for its future role in an organism.

Cell differentiation is crucial for the formation of various tissues and organs in multicellular organisms. For example, stem cells can differentiate into different cell types, such as muscle cells or neurons, depending on the signals they receive from their environment and the particular genes that are activated.

In contrast, determination refers to an earlier stage in this process where a cell's fate is set to become a particular type but has not yet undergone the changes that define full differentiation. Diffusion relates to the passive movement of molecules from areas of high concentration to areas of low concentration and is unrelated to cellular specialization. Diastole describes a phase in the cardiac cycle related to the relaxation of the heart muscle, which again does not pertain to the process of cellular specialization.