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5.9Cloned Animals

Cloned animals have exactly the same genes as the organism from which they were cloned. Two bodies formed from one zygote are examples of cloned animals. Human identical twins are actually naturally occurring cloned humans. In contrast, the cloned animals, which have been much discussed lately, are artificially manufactured (see Chapter 11, Fig. 11-5). They are artificially produced animals in which a nucleus has been taken from a somatic cell and transplanted into an unfertilized egg from which the nucleus has previously been removed. An animal produced in this manner has exactly the same genes as the animal that provided the nucleus, and therefore, it is a cloned animal.
The creation of cloned animals by the above method actually began with an experiment using frogs in 1962. In this experiment, the nucleus of a cell from the tissue of a tadpole was transplanted into an unfertilized frog egg with a destroyed nucleus, and a complete frog was produced. In 1996, the same phenomenon was demonstrated in a mammal by the birth of the cloned sheep "Dolly" (who died of an illness in 2003) (see Chapter 11). This experiment became big news because it was successfully performed on a mammal, and thus, opened the possibility of cloning humans.
Many species of cloned mammals have been created since Dolly, and it is now possible to create a cloned human. However, creating cloned humans is accompanied by many ethical problems, and therefore, it is strictly prohibited in many countries (see Chapter 11). Consequently, there are no authoritative publications about cloned humans. Creation of human clones poses another major problem in addition to these ethical problems, namely that most of the cloned animals created so far have had pathological abnormalities. Therefore, even though this technology is used to improve domestic animals and the like, many problems still need to be solved for efficient cloning of animals.

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