Bone marrow cells that (when signalled) mature into both red blood cells and white blood cells. Receptors on the surface of totipotent stem cells “grasp” passing blood cell growth factors (e.g., Interleukin-7, Stem Cell Growth Factor, etc.), bringing them inside these stem cells and thus causing the maturation and differentiation into red and white blood cells. These receptors are called FLK-Z receptors.