FIGURE 21-10 The pathway from stem cells to lineage-restricted progenitors to differentiated cells. On average, during each division of a multipotent somatic stem cell, at least one of the daughter cells becomes a stem cell like the parent cell. Stem cells thus undergo self-renewal divisions such that the number of stem cells of a particular type stays constant or increases during the organism’s lifetime. Other daughter cells, termed transient amplifying cells, divide rapidly and undergo limited numbers of self-renewal divisions, but ultimately produce lineage-restricted progenitor cells. These cells cannot undergo self-renewal divisions, but can divide and produce differentiated cells of a particular type.