Cloning is the process of making a genetic twin or duplicate of a living organism. The nucleus from one of the organism's cells is taken and implanted in an egg cell (from a different organism) whose nucleus has been removed. The combined cell is stimulated so it begins to divide, and is then implanted in an organic or artificial womb. The resulting organism would be an identical twin -- biologically -- to the nucleus donor.
Cloning has long fascinated science fiction writers and the general public. In science fiction movies, a man is cloned, creating an instant double. In reality, while the clone is a genetic duplicate of the original, the clone is younger. If I clone you, your clone will be a newborn, while you will be whatever age you are now.
Also, although you would be biological duplicates, your clone would have none of your memories. In short, he or she would be a completely different person.
The classic cloning novel in science fiction is Aldous Huxley's Brave New World, published in 1932. In the novel, children are no longer conceived through sexual intercourse but are grown through a combination of artificial insemination of eggs with collected sperm, and cloning, at "hatcheries." Once an egg is fertilized, it is duplicated through "Bokanovsky's Process," cloning 96 genetically identical individuals from the single fertilized egg.
Different batches of cloned embryos are given different nutrients as they develop to create workers with desired characteristics of strength, height, physical attractiveness, and intelligence - alphas, betas, gammas, deltas, and so on. Therefore a person's lot in life is set before they are even born.
Gilbert Gosseyn gets cloned, although the word isn't used, in A.E. van Vogt's The World of Null-A (1945). Ted Thomas and Kate Wilhelm used the word clone in the title of their 1965 novel, The Clone, but the book isn't about human cloning.
In Theodore Sturgeon's "When You Care, When You Love" (1962), an individual is cloned from his cancer cells. The Andrology Institute of America claims they have created clones of dead people by fusing their cells with cow eggs stripped of their DNA. Cows have already been cloned from two-day hold pieces of steak, so it might be possible to clone people from corpses.
Ursula K. LeGuin's "Nine Lives" (1969) is a classic exploration of cloned relationships. Other SF novels with a cloning theme include Pamela Sargent's Cloned Lives (1976), Kate Wilhelm's Where Late the Sweet Birds Sang (1976), Ben Bova's The Multiple Man (1976), John Varley's The Ophiuchi Hotline (1977), and Ray Weldon's The Cloning of Joanna (1989).
Science is quickly catching up with science fiction so far as cloning is concerned. The first clone of a vertebrate was produced in 1967, when British biologist John Gurden successfully cloned a South African clawed frog.
In 1997, Scottish scientist Ian Wilmut and his team successfully cloned an adult mammal. They were the first to accomplish this feat. Wilmut used a small pipette to suck out the nucleus from an unfertilized sheep egg, leaving the egg's cytoplasm empty. The nucleus from another adult sheep -- the subject being cloned -- was placed into the empty egg. Once this was done, the egg contained a complete set of genes, just as if it had been fertilized the natural way, by a sperm. The difference: all the genetic material in the egg was from a single parent -- the animal that donated the nucleus.