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Hans Adolf Edward Dreisch proved that when sea urchin embryonic cells are separated, they can each grow into a complete organism.
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Hans Spemann separated two salamander embryos at a very early age, and they both grew into healthy salamanders. However, he also learned that if they had the embryo had already matured, the twinning would not be successful.
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Sperrman artificially placed the nucleus from an early embryonic cell into a fertilized egg. The egg grew into a fuctional salamander, thus proving that the nucleus of an embryonic cell is responsible for the complete growth of a salamander.
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Robert Briggs and Thomas King transferred the nucleus from an early tadpole embryo into a a frog egg whose nucleus they had removed.
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J. Derek Bromhall successfully transferred the first mammal nucleus into a rabbit egg cell, resulting in a functional rabbit.
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Steen Willadsen placed a fertilized egg into the womb of a female sheep. The sheep gave birth to three live lambs.
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Neal First, Randal Prather, and Willard Eyestone perform the same experiment as Steen Willadsen, except on a cow. It works.
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Ian Wilmut and Keith Campbell take a nucleus from the udder of an adult sheep and implant it into an egg. The resulting sheep is an exact copy of the original.
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Li Meng, John Ely, Richard Stouffer, and Don Wolf clone the first primate. This is majorly important because it decreases the genetic variation in lab animals and shows that primates, and therefore humans, can be cloned.
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Shoukhrat Mitalipov and colleagues cloned human embryonic cells in order to create stem cells for a specific patient.