First published Wed Sep 17, 2008
Dolly, the first mammal cloned from an adult body cell, came into the world as innocent as a lamb; but she has caused panic and controversy, as well as a vast academic and popular literature on the ethics and regulation of cloning. Following the announcement of her birth in February 1997 (Wilmut et al. 1997), an important question arose: if the cloningof mammals is possible, will scientists soon start cloning human beings as well; and if they did, would this be wrong or unwise? More than ten years later, many countries have legally prohibited human cloning or are in the process of doing so, and various institutions, including the United Nations and the European Parliament, are calling for a worldwide ban on all forms of human cloning. Thisentry describes the most important areas of disagreement regarding the ethics of human cloning, since human cloning has been the main topic of the cloning debate.
• • o o o o • o o o o • • • • 1. What is Cloning? 2. Cloning for Research and Therapy 2.1 Creating and Killing Embryos for Stem Cells 2.2 Research Protections and the Need for Oocytes 2.3 Economic and Social Justice Considerations 2.4 ASlippery Slope to Reproductive Cloning 3. Human Reproductive Cloning 3.1 Safety and Efficiency 3.2 Welfare of the Individual Conceived through Cloning 3.3 Effects on Others and Society as a Whole 3.4 Human Dignity 4. Religious perspectives Bibliography Other Internet Resources Related Entries
1. What is Cloning?
Strictly speaking, cloning is the creation of a genetic copy of a sequence of DNA orof the entire genome of an organism. In the latter sense, cloning occurs naturally in the birth of identical twins and other multiples. In the debate over cloning, however, the term ‘cloning’ typically refers to somatic cell nuclear transfer (SCNT). SCNT involves transferring the nucleus of a somatic cell (any
body cell other than a sperm or egg cell) into an enucleated oocyte, i.e. an oocytefrom which the nucleus and thus most of the DNA has been removed. The manipulated oocyte is thereupon treated with chemicals or electric current in order to stimulate cell division and an embryo is formed. Because the embryo's nuclear DNA is that of the somatic cell it is genetically identical to the organism from which the somatic cell was obtained. Dolly the sheep was the first mammal ever tobe cloned using SCNT. Ian Wilmut and his team at the Roslin Institute in Scotland replaced the nucleus from an oocyte taken from a Blackface ewe with the nucleus of a cell from the mammary gland of a six-year old Finn Dorset sheep. They transferred the resulting embryo into the womb of a surrogate ewe and approximately five months later Dolly was born. Dolly had a white face. She was geneticallyidentical to the Finn Dorset ewe from which the somatic cell had been obtained. Dolly, however, was not 100% genetically identical to the donor animal. Genetic material comes from two sources: the nucleus and the mitochondria in the cytoplasm of a cell. Mitochondria are organelles that serve as power sources to the cell. They contain short segments of DNA. In Dolly's case, her nuclear DNA was thesame as the donor animal; other of her genetic materials came from the mitochondria in the cytoplasm of the enucleated oocyte. For the clone and the donor animal to be exact genetic copies, the oocyte too would have to come from the donor animal (or from the same maternal line as mitochondria are passed on by oocytes). Dolly's birth was a real breakthrough, for it proved that something that had beenconsidered biologically impossible could indeed be done. Before Dolly, scientists thought that cell differentiation was irreversible: they believed that, once a cell has differentiated into a specialized body cell, such as a skin or liver cell, the process cannot be reversed. What Dolly demonstrated was that it is possible to take a differentiated cell, turn back its clock, and make the cell...