Cloning started about 50 years ago. There have been many experiments and techniques used. It goes back to 1979 when scientists split mouse embryos in a test tube and then implanted the embryos into the wombs of 2 adult female mice. Not too long after that, they produced genetically identical cows, sheep, and chickens. They did this by moving the nucleus of a cell taken from an early embryo to an egg that has been emptied of its nucleus.