The basic definition of cloning is as follows:
The production of one or more individual plants or animals that are
genetically identical to another plant or animal.There are two procedures that have been referred to as "cloning":
(A.) Embryo cloning
It has been successfully carried out for years on many species of animals. Some experimentation has been done on human embryos. This form of cloning might be more accurately called "artificial twinning", because it stimulates the mechanism by which twins naturally develop. The cloning of embryos started in the 1970's with mice and has been used in animal breeding since the 1980's. The procedure involved the split of a single fertilized ovum into two or more clones, which is then implanted into receptive females. Human embryo cloning begins with a standard in vitro fertilization procedure. Sperm and and egg cell are mixed together on a glass dish. After conception, the zygote (fertilized egg) is allowed to develop into a blastula ( a hollow mass of cells). The zygote divides first into two cells, then four, then eight, etc. A chemical is added to the dish to remove the zona pellucida covering; this material provides nutrients to the cells to promote cell division. Once the "zona pellucida" has been removed, the blastula is divided into individual cells which are deposited on individual dishes. They are then coated with an artificial zona pellucida and allowed to divide and develop.(B.) Adult DNA cloning
has been used to clone a sheep, but has been not tried on humans.The idea has been broached in many medical debates and conferences as a potential treatment for many genetic disorders or even the reproduction of organs for those waiting for organ donors. With the exception of the sperm and egg, every cell in the body contains all of the genetic material in its DNA to theoretically create an exact clone of the original body.
Cloning is as useful as it is destructive, and this is the underlying principle which makes it so controversial. The corresponding web pages to this topic provide an informative view on cloning, its strengths and weaknesses.