ABSTRACT
In this chapter we will study the genetic basis of differentiation and development. Differentiation and development are inextricably linked, but we must not confuse one with the other. Differentiation is the process by which an individual cell acquires a specialized function. Differentiation therefore requires a change in the pattern of gene expression in a cell. The resulting specialized expression pattern usually remains in place for the remainder of the cell’s lifetime and is often inherited by the daughter cells, and the granddaughters, and so on for many cell divisions (Figure 18.1). Development, in contrast, is the pathway that begins with a fertilized egg cell and ends with an adult. A developmental pathway comprises a complex series of genetic, cellular, and physiological events that must occur in the correct order, in the correct cells, and at the appropriate times if the pathway is to reach a successful culmination. These events include the differentiation of many cells into many different specialized types. The human developmental pathway, for example, results in an adult containing 1013 cells differentiated into more than 400 specialized types, with the activity of each individual cell being coordinated with that of every other cell. Understanding how genes specify and regulate the differentiation and developmental pathways of multicellular eukaryotes such as humans is one of the biggest challenges in all of genetics.
