Nuclear transplantation involves the replacement of the nucleus of one cell with that of another. The original purpose of this technique was to test whether the nucleus of a somatic cell can replace the zygote nucleus of a fertilized egg, and so determine whether cell differentiation and morphogenesis are accompanied by stable changes in the genome. The need for such a test was evident since Weismann’s (1892) germ-plasm hypothesis in which it was supposed that genetic determinants are segregated into different cells as development proceeds. The technique of nuclear transfer was first achieved in single-celled organisms, such as Acetabularia (Hammerling, 1934) ?n?Amoeba (Comandon & De Fonbrune, 1939). The delayed-nucleation experiment of Spemann (1938) showed that nuclei are genetically equivalent up to at least the eight-cell stage in amphibia, but was not able to test the reasonable possibility that nuclei might change at later stages when cells...

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