Sorry, web site didn't post; let's try it again!
Http://e science news.com/articles/2009/05/13/what.do.blood.stem.cells.need.grow.blood.flow
just remove the spaces in the main web site portion: "e science news"
Blood type? Blood cells? No matter what question it is, the answer is that it comes from both. If you remember how an embryo is a bunch of cells splitting apart, then you could think of some of those cells as potential blood cells. Simply, blood types are determined by gene dominance, among other things that I probably don't know about (if that was your question).
"In the developing embryo, blood is produced in multiple waves, he noted. In humans, the first red blood cells are produced in the yolk sac. The second wave is produced in the embryonic aorta and those blood stem cells then colonize the liver, which becomes the major blood-producing organ in the fetus."