Clone and Cloning
History Of Cloning
Humans have manipulated plant asexual reproduction through methods like grafting and stem cuttings for more than 2,000 years. The modern era of laboratory cloning began in 1958 when F. C. Steward cloned carrot plants from mature single cells placed in a nutrient culture containing hormones. The first cloning of animal cells took place in 1964 when John B. Gurdon took the nuclei from intestinal cells of toad tadpoles and injected them into unfertilized eggs whose nuclei containing the original parents' genetic information had been destroyed with ultraviolet light. When the eggs were incubated, Gurdon found that 1-2% of the eggs developed into fertile, adult toads.
The first successful cloning of mammals was achieved nearly 20 years later when scientists in both Switzerland and the United States successfully cloned mice using a method similar to Gurdon's approach; but their method required one extra step. After the nuclei were taken from the embryos of one type of mouse, they were transferred into the embryos of another type of mouse who served as a surrogate mother that went through the birthing process to create the cloned mice. The cloning of cattle livestock was achieved in 1988 when nuclei from embryos of prize cows were transplanted to unfertilized cow eggs whose own nuclei had been removed.
In 1997, Scottish scientists cloned a sheep named Dolly, using cells from the mammary glands of an adult sheep and an egg cell from which the nucleus had been removed. This was the first time adult cells, rather than embryonic cells, had been used to clone a mammal. Since then, mice, cattle, goats, and other mammals have been cloned by similar methods. Some of these clones have been genetically altered so that the animals can produce drugs used in human medicine. Scientists are trying to clone organs for human transplant and may soon be able to clone human beings.
In 2001, scientists from Advanced Cell Technology cloned the first endangered animal, a bull gaur (a wild ox from Asia). The newborn died after two days due to infection. Currently, the same group is trying to clone another species of wild cattle, bantengs. In meantime, a group led by P. Loi cloned an endangered mouflon using somatic cells from post-mortem samples.