Fig. 2.

A schematic diagram showing the hierarchy of stem cells from totipotent (able to give rise to entire organism) to pluripotent (able to give rise to any cell type but not entire organism) to so-called adult stem cells, with more limited ability to generate various cell types. The circular arrows shown for totipotent and pluripotent stem cells signify their ability to undergo asymmetric cell division, giving rise to both a daughter stem cell of identical potential and a daughter progenitor cell that is committed to differentiate along a particular cell lineage.