text: Zhong Zhong and Hua Hua were produced by scientists from the Institute of Neuroscience of the Chinese Academy of Sciences in Shanghai, led by Qiang Sun and Mu-ming Poo. They extracted nuclei from the fibroblasts of an aborted fetal monkey (a crab-eating macaque or Macaca fascicularis) and inserted them into egg cells (ova) that had had their own nuclei removed. The team used two enzymes to erase the epigenetic memory of the transferred nuclei of being somatic cells. This crucial reprogramming step allowed the researchers to overcome the main obstacle that had precluded the successful cloning of primates until now. They then placed 21 of these ova into surrogate mother monkeys, resulting in six pregnancies, two of which produced living animals. The monkeys were named Zhong Zhong and Hua Hua, a reference to Zhonghua (, a Chinese name for China). Although the success rate was still low, the methods could be improved to increase survival rate in the future. By comparison, the Scotland-based team that created Dolly the sheep in 1996 required 277 attempts and produced only one lamb.
  The scientists also attempted to clone macaques using nuclei from adult donors, which is much more difficult. They implanted 42 surrogates, resulting in 22 pregnancies, but there were still only two infant macaques, and they died soon after birth.