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Sea Urchin
Hans Adolf Eduard Driesch 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. -
Salamander
Hans Spemann’s first challenge was to figure out how to split the two cells of an embryo much stickier than sea urchin cells, so he 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. -
Salamander Pt. 2
Again using a strand of baby hair tied into a noose, 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, Spemann loosened the noose and let 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. All of the cells grew into a new salamander embryo. -
Frog
Robert Briggs and Thomas King transferred the nucleus from an early tadpole embryo into an enucleated frog egg. The resulting cell developed into a tadpole. -
Frog Pt. 2
John 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. -
Rabbit
J. Derek Bromhall used a glass pipette as a tiny straw to transfer the nucleus from a rabbit embryo cell into an enucleated rabbit egg cell. -
Sheep
Steen Willadsen used a chemical process to separate one cell from an 8-cell lamb embryo. He used a small electrical shock to fuse it to an enucleated egg cell, and the new cell started dividing. -
Cow
Neal First, Randal Prather, and Willard Eyestone used methods very similar to those used by Willadsen on sheep to produce two cloned calves named were Fusion and Copy. -
Sheep Pt. 2
Ian Wilmut and Keith Campbell used cultured sheep cells, which were kept alive in the laboratory rather than the usual donor nuclei from cells in early embryos. They transferred the nuclei from cultured cells into enucleated sheep egg cells. The lambs born from this procedure were named Megan and Morag. -
Sheep Pt. 3 - Dolly
In 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. -
Rhesus Monkey
Li Meng, John Ely, Richard Stouffer, and Don Wolf 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. -
Sheep Pt. 4
Angelika Schnieke, Keith Campbell, and Ian Wilmut introduced the human Factor IX gene into the genome of sheep skin cells grown in a laboratory dish. Factor IX codes for a protein that helps blood clot, and it's used to treat hemophilia. To create the transgenic sheep, the scientists performed nuclear transfer using donor DNA from the cultured transgenic cells. The result was Polly, a sheep that produced Factor IX protein in her milk. -
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Mice, Cows, and Goats
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. Among them were transgenic animals, clones made from fetal and adult cells, and a male mouse; all previous clones had been female. -
Endangered Animals - Gaur and Mouflon
As cloning became more successful, scientists began to create animals belonging to endangered or extinct species. A challenge was finding closely related animals to serve as egg donors and surrogates. The gaur and mouflon were chosen because they're close relatives of domestic cattle and sheep. In 2009, another group of researchers cloned the first extinct animal, a Spanish mountain goat called the bucardo. Unfortunately, the one kid that survived gestation died soon after birth. -
Rhesus Monkey Pt. 2
Shoukhrat Mitalipov and colleagues 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
Shoukhrat Mitalipov and colleagues overcame decades of technical challenges when they 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.