Is cloning useful ?

The asexual creation of a genetic copy, a capability possessed by plants but not by most animals. Thus, plants generate genetic copies spontaneously, and rooting “cuttings” is widely used by horticulturists to propagate millions of clones annually. In animals, only some lower invertebrates can be cloned by “cutting”; for example, earthworms when bisected will regenerate the missing half, resulting in two whole, genetically identical individuals.

However, asexual reproduction and cloning do not normally occur in vertebrates except for the special case of identical twinning. This is despite the fact that individual cells, called blastomeres, within the very early embryo are totipotent; that is, each is capable, if evaluated on its own, of developing into a viable termpregnancy and infant. A major scientific interest in cloning revolves around the question of whether the hereditary material in the nucleus of each cell remains intact throughout development, regardless of the cell’s fate.

On a more practical level, the production of genetic copies of mammals could support the rapid improvement of livestock herds by propagation of valuable founder animals, the creation and production of disease models or transgenic animals for biomedical research, and the preservation of the genetic contribution of a particularly valuable animal, even after death. Therapeutic cloning, a variation that involves the isolation of embryonic stem cells, may provide new cell-based medical approaches to the treatment of human diseases or degenerative conditions. Reproductive cloning. Scientific inquiry into reproductive cloning in animals began with a “fantastical experiment” suggested by Hans Spemann in 1938 that involved the insertion of a nucleus into an ovum bereft of its own genetic material.

This experiment was eventually conducted in 1952 by Robert Briggs and Thomas King in an amphibian, the northern leopard frog, and the technology was quickly extended to a number of other lower vertebrates and invertebrates, and eventually to mammals. The first step in mammalian reproductive cloning is removal of the genetic material from an egg by micromanipulation to create an enucleated egg called a cytoplast. Then genetic material from a donor cell is added, in the form of an intact cell or an isolated nucleus, to produce a diploid, reconstructed embryo.

The cell cycle of the nuclear donor cell may be temporarily slowed or stopped in advance of nuclear transfer. Development of the nuclear transfer embryo is triggered chemically, and the cloned embryo is subsequently transferred into a host mother in order to establish a pregnancy .