"The notion that clones are “identical twins born at different times” is scientifically wrong and very misleading. There is a fundamental distinction between identical twins produced naturally and a SCNT “clone.” Identical twins normally arise by the splitting of an already fertilized egg, so that the two twins share not only the same genetic complement but also have split the cytoplasm from the egg. With SCNT clones, a very different process takes place (Campbell et al. 1996). The egg [from which the nucleus has been removed] comes from one animal, the nuclear material comes from a somatic cell from another animal. This somatic cell is usually fused with the enucleated egg, and then is stimulated electrically or biochemically, while the resulting embryo, if it starts to grow, is then transplanted into the womb of a third animals which acts as the surrogate mother. Thus, a clone of an existing animal will not share the same egg cytoplasm as the original animal, and, while it might share the genes of the original animal, the fact that a nucleus from a somatic cell has been used means that the genes in the somatic cell are subtly different that genes from a fertilized egg. As the FDA notes, the genes in somatic cells need to be reprogrammed so that they are more like fertilized cells. Indeed, research has suggested that, for proper development to occur, a donor nucleus must undergo a reversal of differentiation and a genome-wide epigenetic reprogramming (Riek et al. 2001). Difficulties in this process are believed to be the cause of the high rate of birth defects, and other health problems, in clones. While the FDA acts like a lot is known about epigenetic reprogramming, the reality is that, some ten years after Dolly, there is still a lot that is not know about epigenetic reprogramming which helps explain why the vast majority (e.g. 95%) of cloned embryos do not survive to adulthood."