When nuclei from adult frog cells are transplanted into enucleated eggs, the results have not been so successful. Many of the resulting embryos are abnormal and stop developing. Despite years of effort, no adult frogs have been produced by nuclei transplanted from adult frog cells . No one knows for certain. The DNA becomes chemically altered.
Genes containing methylated DNA are inactive.
So it appears that although every cell in the adult organism contains the entire genome, many of the genes can no longer be expressed. What Dr. Wilmut's group has done is find a way to unlock the full potential of gene expression in the nuclei of cells taken from an adult mammal. They do not know the biochemical basis of their achievement, but this is how they did it. Plunge a micropipette into the egg over the polar body and suck out not only the polar body but the haploid pronucleus within the egg. Fuse each enucleated egg with a diploid cell growing in culture.