The embryo generates two types of cells: somatic cells, which are destined to die, and germ cells, which ensure immortality of the species. These two types of cells are very different. For example, a muscle is a somatic cell, it has a very specialised function and its genetic material will not be passed on to the next generation. On the other hand, the genetic material of germ cells will be inherited. But how can the embryo generate these two strikingly different types of cells? One theory being explored is that the embryo sets aside precursor cells that will not differentiate into somatic cells, but instead maintain totipotency. Totipotency is acquired when a cell can self-renew and retains the capacity to generate any cell of an organism. We now know that chromatin plays an important role in this. Chromatin is made of the genetic material, DNA, wrapped around protein structures called nucleosomes. Interestingly, nucleosomes are ‘decorated’ with chemical modifications, and these give special properties to the genetic material. Cancer cells exploit these modifications to self-renew indefinitely. Thus, at a fundamental level, our research may impact on cancer research.