Genetic Advances
5. Cloning
Cloning
Cloning is the process of creating an exact replica of an organism. The clone’s DNA is exactly the same as the parent’s DNA. Bacteria and plants have long been able to clone themselves through processes of asexual reproduction. In animals, however, cloning does not happen naturally.
Animals can now be cloned in a laboratory, however. In 1997, a sheep named Dolly was the first mammal ever to be successfully cloned. The process of producing an animal like Dolly starts with a single cell from the animal that is going to be cloned. In the case of Dolly, cells from the mammary glands were taken from the adult that was to be cloned. These cells are called somatic, meaning they come from the body and are not gametes like sperm or egg. Remember that somatic cells have a diploid number of chromosomes. Next, the nucleus was removed from this cell. The nucleus was placed in a donor egg that had already had the nucleus removed. The new cell then divided after the stimulation of an electric shock, and development proceeded normally just as if the embryo had formed naturally. The resulting embryo was implanted in a surrogate mother sheep, where it continued its development. This process is shown in Figure below.
To clone an animal, a nucleus from the animals cells are fused with an egg cell (from which the nucleus has been removed) from a donor.
Cloning is not always successful, though. Most of the time, this cloning process does not result in a healthy adult animal. The process has to be repeated many times until it works. In fact, 277 tries were needed to produce Dolly. This high failure rate is one reason that human cloning is banned in the United States. In order to produce a cloned human, many attempts would result in the surrogate mothers experiencing miscarriages, stillbirths, or deformities in the infant. There are also many additional ethical considerations related to human cloning.
CK-12 Foundation, Biology. http://creativecommons.org/licenses/by-nc-sa/3.0/