Where do embryonic stem cells come from?
Embryonic stem cells can be isolated from seven day old embryos. Embryos at this stage are microscopic in size (smaller than the full-stop at the end of this sentence) and consist of a ball of approximately one hundred cells. At this stage the embryo has only two types of cells, those which make the animal or person, and those which will make the tissues which connect the foetus to the mother. Human embryonic stem cells have been isolated from IVF embryos that have been donated by patients at the end of their treatment (so called ‘spare’ IVF embryos), or created from donated eggs and sperm specifically for embryonic stem cell isolation.
