how does a zygote form its own blood?

Question: how does a zygote form its own blood?
- Keywords:
  blood,
  zygote
Asked by dynaset to Byron, David, Esther, Henry, Jacquie on 6 Jul 2017. This question was also asked by 398ylwj1723.
- Jacquie Oliwa answered on 6 Jul 2017:
  
  Hi there,
  Between week 5-6 of pregnancy (the embryonic phase), blood cells begin to form, as does the heart and blood vessels. The first site of blood formation is the yolk sac. Later in embryonic life, the liver becomes the most important red blood cell-forming organ, but it is soon succeeded by the bone marrow, which in adult life is the only source of both red blood cells and the white blood cells.
  
  Both the red and white blood cells arise through a series of complex, gradual, and successive transformations from primitive stem cells. Stem cells are undifferentiated (primitive) cells that can divide to produce offspring cells that can continue to differentiate (become specialized e.g into blood cells, nerve cells etc).
  I hope that answers your question?
  Best wishes,
  Jacquie

Question: how does a zygote form its own blood?