11 July 2008


Cloning in biology is the production of exact copies of an organism or another object, for example, a cell or a gene.

Initially, the word clone (from the Greek. κλων – branch, shoot) was used for a group of plants (for example, fruit trees) obtained vegetatively from a single producer plant. These plants exactly repeated the qualities of their progenitor and could become the founders of a new variety. Later, a clone was called not only the entire group, but also each individual plant in it, and obtaining such descendants was cloning. Over time, the meaning of the term expanded, and it began to be used in microbiology, for the technique of growing cultures of bacteria – descendants of a single cell.

Reproductive cloning of animals, which has become possible thanks to the success of cellular technologies and genetic engineering, attracts the greatest attention of scientists and the public. For reproductive cloning, the method of transferring the somatic cell nucleus (PYASK) into an egg with a removed nucleus is used. Stimulation of its division and introduction into the uterus of a surrogate mother can lead to the birth of an almost identical copy of the donor nucleus (a small part of the hereditary information – the genes of mitochondrial chromosomes – the clone will receive from the cytoplasm of the egg). Unfortunately, due to the complexity of the technique, one healthy clone of any of the mammalian species is obtained at best from 200-300 eggs processed in this way. Nevertheless, since the birth of the famous Dolly sheep, dozens of species of domestic and wild animals have been successfully cloned. In addition to scientific purposes, reproductive cloning can be used to restore extinct or preserve rare species, breed new breeds of animals, etc. Reproductive cloning of primates has not yet been successful, and human cloning, although theoretically possible, is legally prohibited in most countries for ethical reasons.

Therapeutic cloning is a promising method for obtaining stem cells with the properties of embryonic, but genetically identical to the donor nucleus. It is an ideal material for cell therapy, tissue engineering and, in the near future, for growing complex "spare" organs. For several years, the efforts of scientists around the world have focused mainly on attempts to develop a therapeutic cloning technique similar to reproductive cloning. At the same time, an embryo no older than 14 days, consisting of several hundred cells, is destroyed, and embryonic stem cells further develop in cell culture. More recently, two groups of scientists, in Japan and the USA, managed to reprogram adult skin cells – fibroblasts – into cells that practically do not differ from embryonic cells in their ability to transform into any types of cells of the human body using genetic engineering methods. Even Jan Wilmut, the creator of Dolly, announced that he was abandoning attempts at therapeutic cloning by cell nucleus transfer and switching to this new technology.

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