Mammalian development from a single-cell zygote requires extensive cell division, differentiation, and morphogenesis. Coordination between cell division and differentiation is cirital for both embryogenesis and adult homeostasis, and severence of this coordination causes many types of cancer. Despite division kinetics being a fundamental aspect of cell biology, the relative cell cycle lengths of distinct cell types during development and homeostasis remain largely unknown. By using population kinetics (POPKIN) and focusing on cell cycle regulation during development and homeostasis, and tumorigensis, this will increase the understanding of hematopoietic stem cells (HSCs) and their development for regenerative medicine and population dynamics within tumours.