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Contemporary Genetics

Cloning And Stem Cell Research

With increased research in molecular genetics per se two related technologies have come to the fore as centers of ethical concern: cloning and research on embryonic stem cells. Cloning is the process of creating a new organism that is a carbon copy of an already existing organism. In one sense cloning is not a new technology, since bacterial and all other asexually reproducing organisms reproduce in clones (a bacterial colony is a clone, as are tissue cultures that have been used for decades in biological research). What is new in the controversy about cloning in the twenty-first century is the prospect of producing a higher organism such as a mammal or human being from a single cell of an already existing adult organism. In 1997 Dolly the sheep became the most sensational and well-known example of a cloned organism. Dolly was produced by removing the nucleus from the egg cell of one female sheep and causing that enucleated cell to fuse with an adult cell from (with its nucleus intact) a different donor sheep. The new "hybrid" egg cell contained a full set of chromosomes from the donor and thus would develop into a genetic replica of the donor. While transplanting nuclei from one variety of animal to another had been accomplished with amphibians in the early 1950s, nothing of the sort had been accomplished with mammals until the mid-1990s. The advantage of cloning for agriculture is clear: the genetic composition of the offspring is completely predictable (which is not true in conventional breeding methods). The major biological question raised by Dolly was whether cloned organisms are as healthy and long-lived as ones produced by natural fertilization of an egg by a sperm. As it turned out, Dolly showed signs of early aging, a result perhaps of the fact that the donor cell came from a six-year-old ewe, who was already halfway through the sheep's natural life span. The chromosomes of mammals gradually shorten at the ends (telomeres) with aging, a process that is not completely understood but which appears to have important implications for cloning from already aging adult cells.

The leap from Dolly to cloning humans and other mammals (businesses sprang up offering to clone family pets, for example) was quick in coming. Among the ethical problems raised here was the expectation that by having an organism with the same genetic composition it was going to be a replica in every way of the adult from which the donor cell was taken. With humans or pets this meant to many people having a new individual with the same personality and behavioral traits as the donor. Such expectations were based on a simplistic understanding of genetics, especially with regard to complex characteristics such as behavior and personality. One of the important lessons of modern genetic research has been that genes do not unfold automatically into an adult trait. Genes interact with other genes and with the environment to produce a number of variant outcomes, so that a genetic clone would no more behave like its progenitor than any two organisms of the same species.

Cloning humans, of course, raises all sorts of other ethical issues, particularly those surrounding what has come to be known as fetal selection. What does it mean if parents want to control so completely all the physical and physiological, not to say psychological, characteristics of their children? Bioethicists raise the question of how far engineering human traits should be allowed to go. Would it be permissible to clone an embryo from a person who needs a kidney or liver transplant just to get an immunologically compatible organ? Is an embryo produced by cloning really a human being, since it has not been formed by union of egg and sperm? If the answer is yes, then should cloning and bringing the embryo to full term be allowed? Should we be able to clone a terminally ill child in order to provide a replacement? These are not simple questions, but as the technology becomes more certain and available (as it no doubt will) the social and ethical questions must be faced critically and squarely.

Stem cell research poses many of the same problems raised by cloning, but it has a more realistic and immediate medical application as well as some distinct ethical issues of its own. Stem cells are undifferentiated embryo-like cells that are found in various tissues of the adult body. Among the earliest recognized and prolific stem cells are those in bone marrow, but biologists have now found stem cells even in brain tissue that has previously been regarded as incapable of regeneration. What has attracted so much attention about stem cells is that for the most part they have retained the ability to differentiate into a variety of other specialized cells. This is particularly true of embryonic stem cells, which are the most totipotent (capable of differentiation into virtually all other body cell types) of all stem cells. Research into how to culture and deliver stem cells to specific tissues in individuals suffering from particular diseases (for example providing brain stem cells to a person with Alzheimer's or to someone who has suffered brain damage from a stroke) thus offers considerable potential for treating conditions that are now considered incurable. Creating embryos by cloning and growing them just long enough to harvest embryonic stem cells would provide the most ready source of totipotent cells. But many ethicists and religious leaders claim that such embryos are truly human beings and that to grow them only for stem cells, like growing them only for organs and tissues, would amount to murder. Issues like this surfaced after biologists began using existing embryonic stem cell lines for research (derived from frozen embryos left over from fertility clinics) with the result that U.S. President George W. Bush banned the production of any more embryos specifically for the purpose of culturing stem cells (an existing 1993 law had prevented the use of any tax dollars for research on human embryos). The questions of how a human life is defined, at what point in the biological life cycle does it become "human," and, regardless of how we define it, how to form humane social and legal policies regarding early human embryos as research objects are all issues about which there is a great deal of current disagreement. Biomedical researchers and many others think that early embryos (less that twelve weeks) should be available for research purposes, while many political conservatives and religious spokespeople oppose the use of any human embryo that has the capability of developing normally into a fetus. Many countries of Europe, especially England, have been more liberal with their policies regarding embryonic stem cell research, with the consequence that some U.S. researchers have either moved or have contemplated moving their laboratories abroad.

Additional topics

Science EncyclopediaScience & Philosophy: Condensation to CoshContemporary Genetics - Eugenics And The Ethical Issues Of Selective Breeding (1900–1945), Dna, Genomics, And The New Ethical Dilemmas