![]() ![]() Previously, cloned animals had only been produced using cells from embryos. Dolly was the first mammal cloned from a mature cell-in this case, from a donor sheep’s mammary gland. The birth of Dolly the sheep in 1996 was a breakthrough for cloning technology. (Domestic horses were used to carry the pregnancies for both Kurt and the new foal.) None of the animal’s genes changed in the process, so the resulting foal is an identical twin of the original horse-just born at a later time. The egg and donor cell joined together, and the embryo grew in a test tube until it matured enough to be transferred to the surrogate mother’s womb. Taking one of these donor cells, the scientists transferred its nucleus, where the DNA resides, into an egg from a surrogate mother that had been hollowed out to remove its own genetic material. For the Przewalski’s horse clones, scientists used cells that had been collected from a stallion in 1980 and then cryopreserved. Typically, cloning starts by removing a small piece of tissue-usually a skin sample-from a living animal and isolating cells from it in the lab. ![]()
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