Subsequently, the gene can be expressed in the bacterial cell to produce the appropriate protein, which can be used to treat diseases such as diabetes or dwarfism. It has recently become possible to introduce entire cloned functional genes into individuals, treating the disease more directly. Such gene therapy procedures with cloned DNA are likely to be increasingly used in the future.
Clones
Clone is an organism, or group of organisms, derived from another organism by an asexual reproductive process. The word has been applied to cells as well as to organisms, so that a group of cells stemming from a single cell is also called a clone. Usually the members of a clone are identical in their inherited characteristics—that is, in their genes—except for any differences caused by mutation. Identical twins, for example, who originate by the division of a single fertilized egg, are members of a clone; whereas non-identical twins, who derive from two separate fertilized eggs, are not. Besides the organisms known as prokaryotes), a number of other simple organisms such as most protozoans, many other algae, and some yeasts also reproduce by cloning, as do certain higher organisms, for example, flatworms and plants such as the dandelion.
Through recent advances of genetic engineering, scientists can isolate an individual gene from one organism and grow it in another organism belonging to a different species. The species chosen as a recipient is usually one that can reproduce asexually, such as a bacterium or yeast. Thus it is able to produce a clone of organisms, or of cells, that all contain the same foreign gene, or genes. Because bacteria, yeasts, and other cultured cells can multiply rapidly, these methods make possible the production of many copies of a particular gene. The copies can then be isolated and used for the purposes of study or for the purposes of medicine and commerce. This technique is called cloning, because it uses clones of organisms or cells. It has great economic and medical potential and is the subject of active research. Identical-twin animals may be produced by cloning as well. An embryo in the early stage of development is removed from the uterus and split, then each separate part is placed in a surrogate uterus. Mammals such as mice and sheep have been produced in this way.
Another development has been the discovery that a whole nucleus, containing an entire set of chromosomes, can be taken from a cell and injected into a fertilized egg whose own nucleus has been removed. The division of the egg brings about the division of the nucleus, and the descendant nuclei can, in their turn, be injected into eggs. After several such transfers, the nuclei may become capable of directing the development of the eggs into complete organisms genetically identical to the organism from which the original nucleus was taken. This cloning technique is thus, in theory, capable of producing large numbers of genetically identical individuals. Such experiments have been successfully carried out with frogs, mice, and sheep. This technique is known as the “nuclear transfer from cultured cells”. In 1997 the sheep clone named Dolly was created using the DNA from an udder cell of an adult ewe. The DNA was fused with unfertilized egg cells, from which the original chromosomes had been removed. The fused cell developed into an early embryo and was implanted into a surrogate mother.
With developments in animal cloning proceeding, there is now international concern that the private ownership of human genes should be outlawed in order to control and protect the human genetic blueprint.
