After sperm fertilizes an egg, a zygote formes which has the potential to develop into a complete embryo. The fertilized egg is a totipotent stem cell; it has the potential to create any type of cell necessary for embryonic development (this included extraembryonic membranes and tissues, the embryo itself, and all postembryonic tissues and organs). In the first few hours after fertilization, the fertilized egg undergoes several cell divisions that produce identical totipotent cells. ... Stem cells from those stages that match the patients DNA are needed to minimize the danger of rejection. ...

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