The technology of cloning is improving step by step

THIS mouse is one of a batch that represent the latest breakthrough in cloning technology. It was created by Zhao Xiaoyang and Li Wei, of the Chinese Academy of Sciences in Beijing, and their colleagues, and was reported this week in Nature. Cloning mice is nothing new, but this one and 26 like it are descended from what are known as induced pluripotent stem cells. These are created from the laboratory-cultured descendants of normal body cells by activating four usually quiescent genes. The result is something similar to an embryonic stem cell, from which it is already known that new, adult mice can be created. The question is, how similar? Dr Zhao and Dr Li have now shown that the answer is, “very similar indeed”.

To make their clones, Dr Zhao and Dr Li injected induced pluripotent cells into early-stage embryos called blastocysts. Normally, the result of doing this is a chimera—an animal that consists of a mixture of cells derived from the injected cell and the blastocyst. That proves the cells are, indeed, pluripotent; in other words, they can turn into a variety of tissues. But to make a true clone a cell needs to be not just pluripotent, but totipotent and thus able to turn into an entire animal. …