HUMAN CLONING

Human Cloning

Human Cloning

Introduction

Cloning means producing genetically identical organisms, identical either to each other or to some preexisting organism. Human cloning could be used to produce early embryos genetically identical to a patient, in order to derive immunologically compatible stem cells for the treatment of the patient's disease (therapeutic cloning); or, if cloned embryos were transferred to a woman's uterus, they could produce babies genetically identical to each other or to some progenitor (reproductive cloning) (Pedersen & Yanagimachi, 2000).

In 1997, scientists successfully cloned a sheep, Dolly, from the cell of an adult mammal. Cloning involves using the genetic material of an individual to produce a new individual with the exact same genetic features. For years, scientist has been studying animal cloning, and their success has yielded numerous applications, both scientific and commercial. However, those earlier efforts dealt with cloning from an embryo. The cloning of an adult mammal, along with other recent advances in cloning, raises the possibility that the techniques needed to clone human beings are within reach.

The imminence of human cloning inspires hopefulness from its supporters and dismay from its detractors. To both sides in the debate, human cloning would be an unprecedented scientific achievement. However, while supporters say that cloning will bring radical advances in medicine, critics warn that it will open a Pandora's box of irreversible consequences such as mass-produced children and social disintegration (Kind & Colman, 1999).

Discussion

Although cloning is defined in terms of genetic identity, this is usually taken to mean identical with respect to the nuclear genome, disregarding differences in the mitochondrial genome and disregarding also any small differences in nuclear genes that arise during development.

Cloning in animals can arise in two ways. A single fertilized egg can give rise to two fetuses, either by splitting of the embryo before or during implantation in the uterus, or (less frequently) by the formation of two primitive streaks on a single embryonic plate. So-called identical (monozygotic or 'one-egg') twins arise spontaneously in human reproduction; although genetically identical, they are certainly not identical persons. Embryo splitting has been done experimentally in laboratory and farm animals; it has not been carried out in humans (Regalado, 2001).

The other method of artificially producing clones is by nuclear transfer. Nuclei from several cells of an early embryo can each be transferred to an unfertilized egg that has had its own nuclear material removed. After activation, a clone of genetically identical embryos can develop. Cloned sheep (Willadsen, 1986) and cattle have been produced in this way. Once the cells have started to differentiate in the fetus after implantation, cloning can still be carried out, but the success rate is lower. Even adult animals have been cloned, by transfer of nuclei from their somatic cells into enucleated, unfertilized eggs (somatic cell nuclear transfer, SCNT). Dolly, the cloned sheep, was the first, but other animals (cattle, goats, pigs, rabbits, cats) and also mice have now been cloned. Cloning from adult or young animals is 'copying', but the clone, though genetically identical, is ...