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DNA and Genes
The term cloning is used by scientists to describe many
different processes that involve making duplicates of biological
material. In most cases, isolated genes or cells are duplicated for
scientific study, and no new animal results. The experiment that led
to the cloning of Dolly the sheep in 1997 was different: It used a
cloning technique called somatic cell nuclear transfer and
resulted in an animal that was a genetic twin--although delayed in
time--of an adult sheep.
Cloning for Reproductive
Purposes
The technique that produced Dolly was an extension of experiments
that had been ongoing for over 40 years. In the simplest terms, the
technique used to produce Dolly the sheep, somatic cell nuclear
transplantation cloning, involves removing the nucleus of an egg and
replacing it with the diploid nucleus of a somatic cell. Unlike
sexual reproduction, during which a new organism is formed from the
combination of genetic material from an egg and sperm, in nuclear
transplantation cloning there is a single genetic “parent.” This
technique also differs from previous cloning techniques because it
does not involve an existing embryo. Dolly is different because she
is not genetically unique; when born she was genetically identical
to an existing six-year-old ewe. Although the birth of Dolly was
lauded as a success and it did provide new and important insights in
development biology, in fact, the procedure has not been perfected.
It is not yet clear whether Dolly will remain healthy or whether she
is already experiencing subtle problems that might lead to serious
diseases. Thus, the prospect of applying this technique in humans is
troubling for scientific and safety reasons in addition to a variety
of ethical reasons related to our ideas about the natural ordering
of family and successive generations.
Several important concerns remain about the science and safety of
nuclear transfer cloning using adult cells as the source of nuclei.
To date, five mammalian species--sheep, cattle, pigs, goats, and
mice--have been used extensively in reproductive cloning studies.
Data from these experiments illustrate the problems involved.
Typically, very few cloning attempts are successful. Many cloned
animals die in utero, even at late stages of pregnancy or
soon after birth, and those that survive frequently exhibit severe
birth defects. In addition, female animals carrying cloned fetuses
may face serious risks.
An additional concern focuses on whether cellular aging will
affect the ability of somatic cell nuclei to program normal
development. As somatic cells divide, they progressively age, and
there is normally a defined number of cell divisions that can occur
before senescence. Thus, the health effects for the resulting
liveborn, having been created with an "aged" nucleus, are unknown.
Recently researchers reported that Dolly has arthritis, although it
is not yet clear whether the five-and-a-half-year-old sheep is
suffering from the condition as a result of the cloning process.
Scientists in Tokyo have shown that cloned mice die significantly
earlier than those that are naturally conceived, and US scientists
have show that the pattern of gene expression in cloned mice differs
significantly from that observed in naturally conceived mice. These
observations raise concerns about the possible accumulation of
mutations in somatic cells that are transferred in cloning and
possible genetic programming errors.
Ethical Concerns
The announcement of Dolly sparked widespread speculation about a
human child being created using somatic cell nuclear transfer. Much
of the perceived fear that greeted this announcement centered on the
misperception that a child or many children could be produced who
would be identical to an already existing person. This fear is based
on the idea of “genetic determinism”-- that genes alone determine
all aspects of an individual--and reflects the belief that a
person’s genes bear a simple relationship to the physical and
psychological traits that compose that individual. Although genes
play an essential role in the formation of physical and behavioral
characteristics, each individual is, in fact, the result of a
complex interaction between his or her genes and the environment
within which he or she develops. Many of the concerns about cloning
have also focused on issues related to “playing God,” interfering
with the natural order of life, and somehow robbing a future
individual of the right to a unique identity.
Policy and Regulation
Several groups have concluded that reproductive cloning of human
beings creates ethical and scientific risks that society should not
tolerate. In 1997, the National Bioethics Advisory Commission recommended
that it was morally unacceptable to attempt to create a child using
somatic cell nuclear transfer cloning and suggested that a
moratorium be imposed until the safety of this technique could be
assessed. The commission also cautioned against preempting the use
of cloning technology for purposes unrelated to producing a liveborn
child.
Similarly, in 2001 the National Academy of Sciences issued a report
stating that the United States should ban human reproductive cloning
aimed at creating a child because experience with reproductive
cloning in animals suggests that the process would be dangerous for
the woman, the fetus, and the newborn, and would likely fail. The
report recommended that the proposed ban on human cloning should be
reviewed within five years, but that it should be reconsidered "only
if a new scientific review indicates that the procedures are likely
to be safe and effective, and if a broad national dialogue on
societal, religious, and ethical issues suggests that
reconsideration is warranted." The panel concluded that the
scientific and medical considerations that justify a ban on human
reproductive cloning at this time do not apply to nuclear
transplantation to produce stem cells. Several other scientific and
medical groups also have stated their opposition to the use of
cloning for the purpose of producing a child.
In 2002, The President's Council on Bioethics concluded
that reproductive cloning is both unsafe and morally unacceptable
and thus should not be attempted. In reaching this conclusion, the
Council considered concerns about the identity and individuality of
a cloned person, the manufacture of humans, the prospect of a new
eugenics, troubled family relations, and effects on society at
large.
Modified from text provided by the
National Human Genome Research Institute. |
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