How Cloning Works
On Jan. 8, 2001, scientists at Advanced Cell Technology, Inc., announced the birth of the first clone of an endangered animal, a baby bull gaur (a large wild ox from India and southeast Asia) named Noah. Although Noah died of an infection unrelated to the procedure, the experiment demonstrated that it is possible to save endangered species through cloning.
Cloning is the process of making a genetically identical organism through nonsexual means. It has been used for many years to produce plants (even growing a plant from a cutting is a type of cloning).
Animal cloning has been the subject of scientific experiments for years, but garnered little attention until the birth of the first cloned mammal in 1996, a sheep named Dolly. Since Dolly, several scientists have cloned other animals, including cows and mice. The recent success in cloning animals has sparked fierce debates among scientists, politicians and the general public about the use and morality of cloning plants, animals and possibly humans.
In this article, we will examine how cloning works and look at possible uses of this technology.
The unfertilized eggs of some animals (small invertebrates, worms, some species of fish, lizards and frogs) can develop into full-grown adults under certain environmental conditions — usually a chemical stimulus of some kind. This process is calledparthenogenesis, and the offspring are clones of the females that laid the eggs.
Another example of natural cloning is identical twins. Although they are genetically different from their parents, identical twins are naturally occurring clones of each other.
Scientists have experimented with animal cloning, but have never been able to stimulate a specialized (differentiated) cell to produce a new organism directly. Instead, they rely on transplanting the genetic information from a specialized cell into an unfertilized egg cell whose genetic information has been destroyed or physically removed.
In the 1970s, a scientist named John Gurdon successfully cloned tadpoles. He transplanted the nucleus from a specialized cell of one frog (B) into an unfertilized egg of another frog (A) in which the nucleus had been destroyed by ultraviolet light. The egg with the transplanted nucleus developed into a tadpole that was genetically identical to frog B.
While Gurdon’s tadpoles did not survive to grow into adult frogs, his experiment showed that the process of specialization in animal cells was reversible, and his technique of nuclear transfer paved the way for later cloning successes.
In 1996, cloning was revolutionized when Ian Wilmut and his colleagues at the Roslin Institute in Edinburgh, Scotland, successfully cloned a sheep named Dolly. Dolly was the first cloned mammal.
Wilmut and his colleagues transplanted a nucleus from a mammary gland cell of a Finn Dorsett sheep into the enucleated egg of a Scottish blackface ewe. The nucleus-egg combination was stimulated with electricity to fuse the two and to stimulate cell division. The new cell divided and was placed in the uterus of a blackface ewe to develop. Dolly was born months later.
Dolly was shown to be genetically identical to the Finn Dorsett mammary cells and not to the blackface ewe, which clearly demonstrated that she was a successful clone (it took 276 attempts before the experiment was successful). Dolly has since grown and reproduced several offspring of her own through normal sexual means. Therefore, Dolly is a viable, healthy clone.
Since Dolly, several university laboratories and companies have used various modifications of the nuclear transfer technique to produce cloned mammals, including cows, pigs, monkeys, mice and Noah.
read more about Dolly and cloning