In biology, cloning is the process of producing similar populations of genetically identical individuals that occurs in nature when organisms such as bacteria, insects, plants or animals reproduce asexually. Cloning in biotechnology refers to processes used to create copies of DNA fragments (molecular cloning), cells (cell cloning), or organisms (organism cloning). The term also refers to the production of multiple copies of a product such as digital media or software.
Cloning of any DNA fragment essentially involves four steps
- fragmentation – breaking apart a strand of DNA
- ligation – gluing together pieces of DNA in the desired sequence
- transfection – inserting the newly formed pieces of DNA into cells
- screening/selection – selecting out the cells that were successfully transfected with the new DNA
Researchers in China have created two cloned monkeys, the first time that primates have been cloned with the technique that produced Dolly the sheep more than 20 years ago.
The long-tailed macaques, named Zhong Zhong and Hua Hua, were made from fetal cells grown in a petri dish. The clones are identical twins and carry the DNA of the monkey fetus that originally provided the cells, according to a study published in the journal Cell. They were born at the Chinese Academy of Sciences in Shanghai.
Dolly the sheep was produced from udder cells that had been frozen for six years. Until that feat, many researchers had thought that type of cloning was impossible because it required taking adult cells and bringing them back to their original state when sperm first fertilized the egg.
The cell would then have to start to grow in a surrogate’s womb and to differentiate into an entire animal, genetically identical to the one that provided the initial cell.
But once cloning proved possible, researchers began improving their method and testing it on other species. Since Dolly was born, researchers have cloned 23 mammal species, including cattle, cats, deer, dogs, horses, mules, oxen, rabbits and rats.
The genes of cloned monkeys could be manipulated before the process begins, yielding animals that have edited genes in every cell of their bodies, the researchers suggested. This might allow scientists to probe the genes’ functions and to test experimental drugs on monkeys custom-made to have various genetic conditions.
The scientists tried cloning adult cells, but those attempts failed. The older a starting cell, the more difficult it is to clone and the more likely the resulting embryo or fetus will be miscarried in a surrogate female.
If scientists wanted to create a monkey identical to an adult, or even an adolescent, this method so far would not succeed. And the technique used by the Chinese scientists is still a long way from producing human babies, even if that were ethically permissible.