Cloning

1. History

Cloning refers to asexual reproduction, reproduction in absence of germinal cells (Neri 2001: 51). A cloned individual (clone from the Greek Klon: ‘twig’ ‘slip’) may result from two different processes: (1) embryo splitting: this sometimes gives rise to monozygotic twins; and (2) Cell Nuclear Replacement (CNR) or Cell Nuclear Transfer (CNT) technique. This latter was the procedure that produced Dolly (1996–2003). CNR involves two cells: a recipient, which is generally an egg (oocyte), and a donor cell. Early experiments mainly made use of embryonic cells, which were expected to behave similarly to the cells of a fertilized egg, in order to promote normal development after the nuclear replacement. In more recent experiments, the donor cells were taken from either fetal or adult tissues. The nucleus of the donor cell is introduced into the oocyte (either by cell fusion or by injection). With appropriate stimulation – electric pulses or exposure to chemicals – the oocyte is induced to develop. The embryo thus created may be implanted in a viable womb, and in some cases is able to develop to term.

The first experiments on cloning techniques were carried out in Germany at the beginning of the twentieth century. Jacques Loeb and Hans Spemann worked on frogs and sea-urchins. In the late 1970s the first cloned frogs were shown to the world. Experiments on mice and cattle and sheep then began (McLaren 2000). The first cloned creature produced from fetal and adult mammalian cells was reported from an Edinburgh-based group in Nature on 27 February 1997 (Wilmut et al. 1997). ‘Dolly’, now the world’s most famous sheep, caused a sensation and re-awakened the huge popular interest in human attempts to create life by design rather than by a random combination of genes. Cloning has become one of the most hotly debated and least well-understood phenomena in contemporary science, let alone contemporary bioethics.