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First demonstration of artificial embryo twinning
Dreisch showed that by merely shaking two-celled sea urchin embryos, it was possible to separate the cells. Once separated, each cell grew into a complete sea urchin. -
Artificial embryo twinning in a vertebrate
Spemann fashioned a tiny noose from a strand of baby hair and tightened it between two cells of a salamander embryo until they separated. Each cell grew into an adult salamander. -
The cell nucleus controls embryonic development
Spemann temporarily squeezed a fertilized salamander egg to push the nucleus to one side of the cytoplasm. The egg divided into cells—but only on the side with the nucleus. After four cell divisions, which made 16 cells, Spemann loosened the noose, letting the nucleus from one of the cells slide back into the non-dividing side of the egg. He used the noose to separate this “new” cell from the rest of the embryo. The single cell grew into a new salamander embryo, as did the remaining cells that w -
First successful nuclear transfer
Briggs and King transferred the nucleus from an early tadpole embryo into an enucleated frog egg (a frog egg from which the nucleus had been removed). The resulting cell developed into a tadpole. -
Nuclear transfer from a differentiated cell
Gurdon transplanted the nucleus of a tadpole intestinal cell into an enucleated frog egg. In this way, he created tadpoles that were genetically identical to the one from which the intestinal cell was taken. -
First mammalian embryo created by nuclear transfer
Mammalian egg cells are much smaller than those of frogs or salamanders, so they are harder to manipulate. Using a glass pipette as a tiny straw, Bromhall transferred the nucleus from a rabbit embryo cell into an enucleated rabbit egg cell. He considered the procedure a success when a morula, or advanced embryo, developed after a couple of days. -
First mammal created by nuclear transfer
Willadsen used a chemical process to separated one cell from an 8-cell lamb embryo. The he used a small electrical shock to fuse it to an enucleated egg cell. As luck would have it, the new cell started dividing. -
Nuclear transfer from embryonic cell
Using methods very similar to those used by Willadsen on sheep, First, Prather, and Eyestone produced two cloned calves. Their names were Fusion and Copy. -
Nuclear transfer from laboratory cells
All previous cloning experiments used donor nuclei from cells in early embryos. In this experiment, the donor nuclei came from a slightly different source: cultured sheep cells, which were kept alive in the laboratory. Wilmut and Campbell transferred the nuclei from cultured cells into enucleated sheep egg cells. The lambs born from this procedure were named Megan and Morag. -
Dolly: First mammal created by somatic cell nuclear transfer
n this landmark experiment, Wilmut and Campbell created a lamb by transferring the nucleus from an adult sheep's udder cell into an enucleated egg. Never before had a mammal been cloned from an adult somatic cell. -
First primate created by embryonic cell nuclear transfer
Similar to previous cloning experiments, Wolf’s team of scientists fused early-stage embryonic cells with enucleated monkey egg cells using a small electrical shock. The resulting embryos were then implanted into surrogate mothers. Out of 29 cloned embryos, two monkeys were born. One was a female named Neti, and the other was a male named Ditto. -
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More mammals cloned by somatic cell nuclear transfer
After the successes leading up to Dolly and Polly, other scientists wanted to see if similar techniques could be used to clone other mammalian species. Before long, several more animals had been successfully cloned. -
Endangered animals cloned by somatic cell nuclear transfer
As the list of successfully cloned animals grew, scientists began to explore cloning as a way to create animals belonging to endangered or extinct species. A challenge to cloning endangered and extinct species is finding closely related animals to serve as egg donors and surrogates. The gaur and mouflon were chosen in part because they are close relatives of domestic cattle and sheep, respectively. -
Primate embryonic stem cells created by somatic cell nuclear transfer
Researchers took a cell from an adult monkey and fused it with an enucleated egg cell. The embryo was allowed to develop for a time, then its cells were grown in a culture dish. These cells, because they can differentiate to form any cell type, are called embryonic stem cells. -
Human embryonic stem cells created by somatic cell nuclear transfer
Overcoming decades of technical challenges, Mitalipov and colleagues were the first to use somatic cell nuclear transfer to create a human embryo that could be used as a source of embryonic stem cells. The resulting stem cell lines were specific to the patient they came from, a baby with a rare genetic disorder.
