What are the benefits of human genetic engineering?
The benefits of human genetic engineering can be found in the headlines nearly every day. With
the successful cloning of mammals and the completion of the Human Genome Project, scientists
all over the world are aggressively researching the many different facets of human genetic
engineering. These continuing breakthroughs have allowed science to more deeply understand
DNA and its role in medicine, pharmacology, reproductive technology, and countless other fields.
The most promising benefit of human genetic engineering is gene therapy. Gene therapy is the
medical treatment of a disease by repairing or replacing defective genes or introducing
therapeutic genes to fight the disease. Over the past ten years, certain autoimmune diseases and
heart disease have been treated with gene therapy. Many diseases, such as Huntington's
disease, ALS (Lou Gehrig's disease), and cystic fibrosis are caused by a defective gene. The
hope is that soon, through genetic engineering, a cure can be found for these diseases by either
inserting a corrected gene, modifying the defective gene, or even performing genetic surgery.
Eventually the hope is to completely eliminate certain genetic diseases as well as treat nongenetic diseases with an appropriate gene therapy.
Currently, many pregnant women elect to have their fetuses screened for genetic defects. The
results of these screenings can allow the parents and their physician to prepare for the arrival of a
child who may have special needs before, during, and after delivery. One possible future benefit
of human genetic engineering is that, with gene therapy, a fetus w/ a genetic defect could be
treated and even cured before it is born. There is also current research into gene therapy for
embryos before they are implanted into the mother through in-vitro fertilization.
Another benefit of genetic engineering is the creation pharmaceutical products that are superior
to their predecessors. These new pharmaceuticals are created through cloning certain genes.
Currently on the market are bio-engineered insulin (which was previously obtained from sheep or
cows) and human growth hormone (which in the past was obtained from cadavers) as well as bioengineered hormones and blood clotting factors. The hope in the future is to be able to create
plants or fruits that contain a certain drug by manipulating their genes in the laboratory.
The field of human genetic engineering is growing and changing at a tremendous pace. With
these changes come several benefits and risks. These benefits and risks must be weighed in light
of their moral, spiritual, legal, and ethical perspectives. The potential power of human genetic
engineering comes with great responsibility.
Human Genetic Engineering
Dr. Ray Bohlin
What forms of genetic engineering can be done in human beings?
Genetic technology harbors the potential to change the human species forever. The soon
to be completed Human Genome Project will empower genetic scientists with a human
biological instruction book. The genes in all our cells contain the code for proteins that
provide the structure and function to all our tissues and organs. Knowing this complete
code will open new horizons for treating and perhaps curing diseases that have remained
mysteries for millennia. But along with the commendable and compassionate use of
genetic technology comes the specter of both shadowy purposes and malevolent aims.
For some, the potential for misuse is reason enough for closing the door completely--the
benefits just aren't worth the risks. In this article, I'd like to explore the application of
genetic technology to human beings and apply biblical wisdom to the eventual ethical
quagmires that are not very far away. In this section we'll investigate the various ways
humans can be engineered.
Since we have introduced foreign genes into the embryos of mice, cows, sheep, and pigs
for years, there's no technological reason to suggest that it can't be done in humans too.
Currently, there are two ways of pursuing gene transfer. One is simply to attempt to
alleviate the symptoms of a genetic disease. This entails gene therapy, attempting to
transfer the normal gene into only those tissues most affected by the disease. For
instance, bronchial infections are the major cause of early death for patients with cystic
fibrosis (CF). The lungs of CF patients produce thick mucus that provides a great growth
medium for bacteria and viruses. If the normal gene can be inserted in to the cells of the
lungs, perhaps both the quality and quantity of their life can be enhanced. But this is not a
complete cure and they will still pass the CF gene on to their children.
In order to cure a genetic illness, the defective gene must be replaced throughout the
body. If the genetic defect is detected in an early embryo, it's possible to add the gene at
this stage, allowing the normal gene to be present in all tissues including reproductive
tissues. This technique has been used to add foreign genes to mice, sheep, pigs, and cows.
However, at present, no laboratory is known to be attempting this well-developed
technology in humans. Princeton molecular biologist Lee Silver offers two reasons.{1}
First, even in animals, it only works 50% of the time. Second, even when successful,
about 5% of the time, the new gene gets placed in the middle of an existing gene, creating
a new mutation. Currently these odds are not acceptable to scientists and especially
potential clients hoping for genetic engineering of their offspring. But these are only
problems of technique. It's reasonable to assume that these difficulties can be overcome
with further research.
Should genetic engineering be used for curing genetic diseases?
The primary use for human genetic engineering concerns the curing of genetic disease.
But even this should be approached cautiously. Certainly within a Christian worldview,
relieving suffering wherever possible is to walk in Jesus' footsteps. But what diseases?
How far should our ability to interfere in life be allowed to go? So far gene therapy is
primarily tested for debilitating and ultimately fatal diseases such as cystic fibrosis.
The first gene therapy trial in humans corrected a life-threatening immune disorder in a
two-year-old girl who, now ten years later, is doing well. The gene therapy required
dozens of applications but has saved the family from a $60,000 per year bill for necessary
drug treatment without the gene therapy.{2} Recently, sixteen heart disease patients, who
were literally waiting for death, received a solution containing copies of a gene that
triggers blood vessel growth by injection straight into the heart. By growing new blood
vessels around clogged arteries, all sixteen showed improvement and six were completely
relieved of pain.
In each of these cases, gene therapy was performed as a last resort for a fatal condition.
This seems to easily fall within the medical boundaries of seeking to cure while at the
same time causing no harm. The problem will arise when gene therapy will be sought to
alleviate a condition that is less than life-threatening and perhaps considered by some to
simply be one of life's inconveniences, such as a gene that may offer resistance to AIDS
or may enhance memory. Such genes are known now and many are suggesting that these
goals will and should be available for gene therapy.
The most troublesome aspect of gene therapy has been determining the best method of
delivering the gene to the right cells and enticing them to incorporate the gene into the
cell's chromosomes. Most researchers have used crippled forms of viruses that naturally
incorporate their genes into cells. The entire field of gene therapy was dealt a severe
setback in September 1999 upon the death of Jesse Gelsinger who had undergone gene
therapy for an inherited enzyme deficiency at the University of Pennsylvania.{3} Jesse
apparently suffered a severe immune reaction and died four days after being injected with
the engineered virus.
The same virus vector had been used safely in thousands of other trials, but in this case,
after releasing stacks of clinical data and answering questions for two days, the
researchers didn't fully understand what had gone wrong.{4} Other institutions were also
found to have failed to file immediate reports as required of serious adverse events in
their trials, prompting a congressional review.{5} All this should indicate that the
answers to the technical problems of gene therapy have not been answered and progress
will be slowed as guidelines and reporting procedures are studied and reevaluated.
Will correcting my genetic problem, prevent it in my descendants?
The simple answer is no, at least for the foreseeable future. Gene therapy currently targets
existing tissue in a existing child or adult. This may alleviate or eliminate symptoms in
that individual, but will not affect future children. To accomplish a correction for future
generations, gene therapy would need to target the germ cells, the sperm and egg. This
poses numerous technical problems at the present time. There is also a very real concern
about making genetic decisions for future generations without their consent.
Some would seek to get around these difficulties by performing gene therapy in early
embryos before tissue differentiation has taken place. This would allow the new gene to
be incorporated into all tissues, including reproductive organs. However, this process
does nothing to alleviate the condition of those already suffering from genetic disease.
Also, as mentioned earlier this week, this procedure would put embryos at unacceptable
risk due to the inherent rate of failure and potential damage to the embryo.
Another way to affect germ line gene therapy would involve a combination of gene
therapy and cloning.{6} An embryo, fertilized in vitro, from the sperm and egg of a
couple at risk for sickle-cell anemia, for example, could be tested for the sickle-cell gene.
If the embryo tests positive, cells could be removed from this early embryo and grown in
culture. Then the normal hemoglobin gene would be added to these cultured cells.
If the technique for human cloning could be perfected, then one of these cells could be
cloned to create a new individual. If the cloning were successful, the resulting baby
would be an identical twin of the original embryo, only with the sickle-cell gene replaced
with the normal hemoglobin gene. This would result in a normal healthy baby.
Unfortunately, the initial embryo was sacrificed to allow the engineering of its identical
twin, an ethically unacceptable trade-off.
So what we have seen, is that even human gene therapy is not a long-term solution, but a
temporary and individual one. But even in condoning the use of gene therapy for
therapeutic ends, we need to be careful that those for whom gene therapy is unavailable
either for ethical or monetary reasons, don't get pushed aside. It would be easy to shun
those with uncorrected defects as less than desirable or even less than human. There is,
indeed, much to think about.
Should genetic engineering be used to produce super-humans?
The possibility of someone or some government utilizing the new tools of genetic
engineering to create a superior race of humans must at least be considered. We need to
emphasize, however, that we simply do not know what genetic factors determine
popularly desired traits such as athletic ability, intelligence, appearance and personality.
For sure, each of these has a significant component that may be available for genetic
manipulation, but it's safe to say that our knowledge of each of these traits is in its
infancy.
Even as knowledge of these areas grows, other genetic qualities may prevent their
engineering. So far, few genes have only a single application in the body. Most genes are
found to have multiple effects, sometimes in different tissues. Therefore, to engineer a
gene for enhancement of a particular trait--say memory--may inadvertently cause
increased susceptibility to drug addiction.
But what if in the next 50 to 100 years, many of these unknowns can be anticipated and
engineering for advantageous traits becomes possible. What can we expect? Our concern
is that without a redirection of the world view of the culture, there will be a growing
propensity to want to take over the evolution of the human species. The many people see
it, we are simply upright, large-brained apes. There is no such thing as an independent
mind. Our mind becomes simply a physical construct of the brain. While the brain is
certainly complicated and our level of understanding of its intricate machinery grows
daily, some hope that in the future we may comprehend enough to change who and what
we are as a species in order to meet the future demands of survival.
Edward O. Wilson, a Harvard entomologist, believes that we will soon be faced with
difficult genetic dilemmas. Because of expected advances in gene therapy, we will not
only be able to eliminate or at least alleviate genetic disease, we may be able to enhance
certain human abilities such as mathematics or verbal ability. He says, "Soon we must
look deep within ourselves and decide what we wish to become."{7} As early as 1978,
Wilson reflected on our eventual need to "decide how human we wish to remain."{8}
Surprisingly, Wilson predicts that future generations will opt only for repair of disabling
disease and stop short of genetic enhancements. His only rationale however, is a question.
"Why should a species give up the defining core of its existence, built by millions of
years of biological trial and error?"{9} Wilson is naively optimistic. There are loud
voices already claiming that man can intentionally engineer our "evolutionary" future
better than chance mutations and natural selection. The time to change the course of this
slow train to destruction is now, not later.
Should I be able to determine the sex of my child?
Many of the questions surrounding the ethical use of genetic engineering practices are
difficult to answer with a simple yes or no. This is one of them. The answer revolves
around the method used to determine the sex selection and the timing of the selection
itself.
For instance, if the sex of a fetus is determined and deemed undesirable, it can only be
rectified by termination of the embryo or fetus, either in the lab or in the womb by
abortion. There is every reason to prohibit this process. First, an innocent life has been
sacrificed. The principle of the sanctity of human life demands that a new innocent life
not be killed for any reason apart from saving the life of the mother. Second, even in this
country where abortion is legal, one would hope that restrictions would be put in place to
prevent the taking of a life simply because it's the wrong sex.
However, procedures do exist that can separate sperm that carry the Y chromosome from
those that carry the X chromosome. Eggs fertilized by sperm carrying the Y will be male,
and eggs fertilized by sperm carrying the X will be female. If the sperm sample used to
fertilize an egg has been selected for the Y chromosome, you simply increase the odds of
having a boy (~90%) over a girl. So long as the couple is willing to accept either a boy or
girl and will not discard the embryo or abort the baby if it's the wrong sex, it's difficult to
say that such a procedure should be prohibited.
One reason to utilize this procedure is to reduce the risk of a sex-linked genetic disease.
Color-blindness, hemophilia, and fragile X syndrome can be due to mutations on the X
chromosome. Therefore, males (with only one X chromosome) are much more likely to
suffer from these traits when either the mother is a carrier or the father is affected. (In
females, the second X chromosome will usually carry the normal gene, masking the
mutated gene on the other X chromosome.) Selecting for a girl by sperm selection greatly
reduces the possibility of having a child with either of these genetic diseases. Again, it's
difficult to argue against the desire to reduce suffering when a life has not been forfeited.
But we must ask, is sex determination by sperm selection wise? A couple that already has
a boy and simply wants a girl to balance their family, seems innocent enough. But why is
this important? What fuels this desire? It's dangerous to take more and more control over
our lives and leave the sovereignty of God far behind. This isn't a situation of life and
death or even reducing suffering.
But while it may be difficult to find anything seriously wrong with sex selection, it's also
difficult to find anything good about it. Even when the purpose may be to avoid a sexlinked disease, we run the risk of communicating to others affected by these diseases that
because they could have been avoided, their life is somehow less valuable. So while it
may not be prudent to prohibit such practices, it certainly should not be approached
casually either.
Cloning Fact Sheet
Introduction
The possibility of human cloning, raised when Scottish scientists at Roslin Institute
created the much-celebrated sheep "Dolly" (Nature 385, 810-13, 1997), aroused
worldwide interest and concern because of its scientific and ethical implications. The
feat, cited by Science magazine as the breakthrough of 1997, also generated uncertainty
over the meaning of "cloning" --an umbrella term traditionally used by scientists to
describe different processes for duplicating biological material.
What is cloning? Are there different types of cloning?
When the media report on cloning in the news, they are usually talking about only one
type called reproductive cloning. There are different types of cloning however, and
cloning technologies can be used for other purposes besides producing the genetic twin of
another organism. A basic understanding of the different types of cloning is key to taking
an informed stance on current public policy issues and making the best possible personal
decisions. The following three types of cloning technologies will be discussed: (1)
recombinant DNA technology or DNA cloning, (2) reproductive cloning, and (3)
therapeutic cloning.
Recombinant DNA Technology or DNA Cloning
The terms "recombinant DNA technology," "DNA cloning," "molecular cloning," and
"gene cloning" all refer to the same process: the transfer of a DNA fragment of
interest from one organism to a self-replicating genetic element such as a bacterial
plasmid. The DNA of interest can then be propagated in a foreign host cell. This
technology has been around since the 1970s, and it has become a common practice
in molecular biology labs today.
Scientists studying a particular gene often use bacterial plasmids to generate multiple
copies of the same gene. Plasmids are self-replicating extra-chromosomal circular DNA
molecules, distinct from the normal bacterial genome (see image to the right). Plasmids
and other types of cloning vectors were used by Human Genome Project researchers to
copy genes and other pieces of chromosomes to generate enough identical material for
further study.
To "clone a gene," a DNA fragment containing the gene of interest is isolated from
chromosomal DNA using restriction enzymes and then united with a plasmid that has
been cut with the same restriction enzymes. When the fragment of chromosomal DNA is
joined with its cloning vector in the lab, it is called a "recombinant DNA molecule."
Following introduction into suitable host cells, the recombinant DNA can then be
reproduced along with the host cell DNA. See a diagram depicting this process.
Plasmids can carry up to 20,000 bp of foreign DNA. Besides bacterial plasmids, some
other cloning vectors include viruses, bacteria artificial chromosomes (BACs), and yeast
artificial chromosomes (YACs). Cosmids are artificially constructed cloning vectors that
carry up to 45 kb of foreign DNA and can be packaged in lambda phage particles for
infection into E. coli cells. BACs utilize the naturally occurring F-factor plasmid found in
E. coli to carry 100- to 300-kb DNA inserts. A YAC is a functional chromosome derived
from yeast that can carry up to 1 MB of foreign DNA. Bacteria are most often used as the
host cells for recombinant DNA molecules, but yeast and mammalian cells also are used.
Reproductive Cloning
Reproductive cloning is a technology used to
generate an animal that has the same nuclear DNA
as another currently or previously existing animal.
Dolly was created by reproductive cloning
technology. In a process called "somatic cell
nuclear transfer" (SCNT), scientists transfer genetic
material from the nucleus of a donor adult cell to an
egg whose nucleus, and thus its genetic material,
has been removed. The reconstructed egg
containing the DNA from a donor cell must be
treated with chemicals or electric current in order to
stimulate cell division. Once the cloned embryo
reaches a suitable stage, it is transferred to the
uterus of a female host where it continues to
develop until birth.
Celebrity Sheep Died at
Age 6
Dolly, the first mammal to
be cloned from adult DNA,
was put down by lethal
injection Feb. 14, 2003. Prior to her death,
Dolly had been suffering from lung cancer
and crippling arthritis. Although most Finn
Dorset sheep live to be 11 to 12 years of
age, postmortem examination of Dolly
seemed to indicate that, other than her
cancer and arthritis, she appeared to be
quite normal. The unnamed sheep from
which Dolly was cloned had died several
years prior to her creation. Dolly was a
mother to six lambs, bred the old-fashioned
way.
Image credit: Roslin Institute Image Library
Dolly or any other animal created using nuclear
transfer technology is not truly an identical clone of the donor animal. Only the clone's
chromosomal or nuclear DNA is the same as the donor. Some of the clone's genetic
materials come from the mitochondria in the cytoplasm of the enucleated egg.
Mitochondria, which are organelles that serve as power sources to the cell, contain their
own short segments of DNA. Acquired mutations in mitochondrial DNA are believed to
play an important role in the aging process.
Dolly's success is truly remarkable because it proved that the genetic material from a
specialized adult cell, such as an udder cell programmed to express only those genes
needed by udder cells, could be reprogrammed to generate an entire new organism.
Before this demonstration, scientists believed that once a cell became specialized as a
liver, heart, udder, bone, or any other type of cell, the change was permanent and other
unneeded genes in the cell would become inactive. Some scientists believe that errors or
incompleteness in the reprogramming process cause the high rates of death, deformity,
and disability observed among animal clones.
Therapeutic Cloning
Therapeutic cloning, also called "embryo cloning," is the production of human embryos
for use in research. The goal of this process is not to create cloned human beings, but
rather to harvest stem cells that can be used to study human development and to treat
disease. Stem cells are important to biomedical researchers because they can be used to
generate virtually any type of specialized cell in the human body. Stem cells are extracted
from the egg after it has divided for 5 days. The egg at this stage of development is called
a blastocyst. The extraction process destroys the embryo, which raises a variety of ethical
concerns. Many researchers hope that one day stem cells can be used to serve as
replacement cells to treat heart disease, Alzheimer's, cancer, and other diseases. See more
on the potential use of cloning in organ transplants.
In November 2001, scientists from Advanced Cell Technologies (ACT), a biotechnology
company in Massachusetts, announced that they had cloned the first human embryos for
the purpose of advancing therapeutic research. To do this, they collected eggs from
women's ovaries and then removed the genetic material from these eggs with a needle
less than 2/10,000th of an inch wide. A skin cell was inserted inside the enucleated egg to
serve as a new nucleus. The egg began to divide after it was stimulated with a chemical
called ionomycin. The results were limited in success. Although this process was carried
out with eight eggs, only three began dividing, and only one was able to divide into six
cells before stopping.
How can cloning technologies be used?
Recombinant DNA technology is important for learning about other related technologies,
such as gene therapy, genetic engineering of organisms, and sequencing genomes. Gene
therapy can be used to treat certain genetic conditions by introducing virus vectors that
carry corrected copies of faulty genes into the cells of a host organism. Genes from
different organisms that improve taste and nutritional value or provide resistance to
particular types of disease can be used to genetically engineer food crops. See Genetically
Modified Foods and Organisms for more information. With genome sequencing,
fragments of chromosomal DNA must be inserted into different cloning vectors to
generate fragments of an appropriate size for sequencing. See a diagram on constructing
clones for sequencing.
If the low success rates can be improved (Dolly was only one success out of 276 tries),
reproductive cloning can be used to develop efficient ways to reliably reproduce animals
with special qualities. For example, drug-producing animals or animals that have been
genetically altered to serve as models for studying human disease could be mass
produced.
Reproductive cloning also could be used to repopulate endangered animals or animals
that are difficult to breed. In 2001, the first clone of an endangered wild animal was born,
a wild ox called a gaur. The young gaur died from an infection about 48 hours after its
birth. In 2001, scientists in Italy reported the successful cloning of a healthy baby
mouflon, an endangered wild sheep. The cloned mouflon is living at a wildlife center in
Sardinia. Other endangered species that are potential candidates for cloning include the
African bongo antelope, the Sumatran tiger, and the giant panda. Cloning extinct animals
presents a much greater challenge to scientists because the egg and the surrogate needed
to create the cloned embryo would be of a species different from the clone.
Therapeutic cloning technology may some day be used in humans to produce whole
organs from single cells or to produce healthy cells that can replace damaged cells in
degenerative diseases such as Alzheimer's or Parkinson's. Much work still needs to be
done before therapeutic cloning can become a realistic option for the treatment of
disorders.
What animals have been cloned?
Scientists have been cloning animals for many years. In 1952, the first animal, a tadpole,
was cloned. Before the creation of Dolly, the first mammal cloned from the cell of an
adult animal, clones were created from embryonic cells. Since Dolly, researchers have
cloned a number of large and small animals including sheep, goats, cows, mice, pigs,
cats, rabbits, and a gaur. See Cloned Animals below. All these clones were created using
nuclear transfer technology.
Hundreds of cloned animals exist today, but the number of different species is limited.
Attempts at cloning certain species have been unsuccessful. Some species may be more
resistant to somatic cell nuclear transfer than others. The process of stripping the nucleus
from an egg cell and replacing it with the nucleus of a donor cell is a traumatic one, and
improvements in cloning technologies may be needed before many species can be cloned
successfully.
Can organs be cloned for use in transplants?
Scientists hope that one day therapeutic cloning can be used to generate tissues and
organs for transplants. To do this, DNA would be extracted from the person in need of a
transplant and inserted into an enucleated egg. After the egg containing the patient's DNA
starts to divide, embryonic stem cells that can be transformed into any type of tissue
would be harvested. The stem cells would be used to generate an organ or tissue that is a
genetic match to the recipient. In theory, the cloned organ could then be transplanted into
the patient without the risk of tissue rejection. If organs could be generated from cloned
human embryos, the need for organ donation could be significantly reduced.
Many challenges must be overcome before "cloned organ" transplants become reality.
More effective technologies for creating human embryos, harvesting stem cells, and
producing organs from stem cells would have to be developed. In 2001, scientists with
the biotechnology company Advanced Cell Technology (ACT) reported that they had
cloned the first human embryos; however, the only embryo to survive the cloning process
stopped developing after dividing into six cells. In February 2002, scientists with the
same biotech company reported that they had successfully transplanted kidney-like
organs into cows. The team of researchers created a cloned cow embryo by removing the
DNA from an egg cell and then injecting the DNA from the skin cell of the donor cow's
ear. Since little is known about manipulating embryonic stem cells from cows, the
scientists let the cloned embryos develop into fetuses. The scientists then harvested fetal
tissue from the clones and transplanted it into the donor cow. In the three months of
observation following the transplant, no sign of immune rejection was observed in the
transplant recipient.
Another potential application of cloning to organ transplants is the creation of genetically
modified pigs from which organs suitable for human transplants could be harvested . The
transplant of organs and tissues from animals to humans is called xenotransplantation.
Why pigs? Primates would be a closer match genetically to humans, but they are more
difficult to clone and have a much lower rate of reproduction. Of the animal species that
have been cloned successfully, pig tissues and organs are more similar to those of
humans. To create a "knock-out" pig, scientists must inactivate the genes that cause the
human immune system to reject an implanted pig organ. The genes are knocked out in
individual cells, which are then used to create clones from which organs can be
harvested. In 2002, a British biotechnology company reported that it was the first to
produce "double knock-out" pigs that have been genetically engineered to lack both
copies of a gene involved in transplant rejection. More research is needed to study the
transplantation of organs from "knock-out" pigs to other animals.
What are the risks of cloning?
Reproductive cloning is expensive and highly inefficient. More than 90% of cloning
attempts fail to produce viable offspring. More than 100 nuclear transfer procedures
could be required to produce one viable clone. In addition to low success rates, cloned
animals tend to have more compromised immune function and higher rates of infection,
tumor growth, and other disorders. Japanese studies have shown that cloned mice live in
poor health and die early. About a third of the cloned calves born alive have died young,
and many of them were abnormally large. Many cloned animals have not lived long
enough to generate good data about how clones age. Appearing healthy at a young age
unfortunately is not a good indicator of long-term survival. Clones have been known to
die mysteriously. For example, Australia's first cloned sheep appeared healthy and
energetic on the day she died, and the results from her autopsy failed to determine a cause
of death.
In 2002, researchers at the Whitehead Institute for Biomedical Research in Cambridge,
Massachusetts, reported that the genomes of cloned mice are compromised. In analyzing
more than 10,000 liver and placenta cells of cloned mice, they discovered that about 4%
of genes function abnormally. The abnormalities do not arise from mutations in the genes
but from changes in the normal activation or expression of certain genes.
Problems also may result from programming errors in the genetic material from a donor
cell. When an embryo is created from the union of a sperm and an egg, the embryo
receives copies of most genes from both parents. A process called "imprinting"
chemically marks the DNA from the mother and father so that only one copy of a gene
(either the maternal or paternal gene) is turned on. Defects in the genetic imprint of DNA
from a single donor cell may lead to some of the developmental abnormalities of cloned
embryos.
For more details on the risks associated with cloning, see the Cloning Problems links
below.
Should humans be cloned?
Physicians from the American Medical Association and scientists with the American
Association for the Advancement of Science have issued formal public statements
advising against human reproductive cloning. The U.S. Congress has considered the
passage of legislation that could ban human cloning. See the Policy and Legislation links
below.
Due to the inefficiency of animal cloning (only about 1 or 2 viable offspring for every
100 experiments) and the lack of understanding about reproductive cloning, many
scientists and physicians strongly believe that it would be unethical to attempt to clone
humans. Not only do most attempts to clone mammals fail, about 30% of clones born
alive are affected with "large-offspring syndrome" and other debilitating conditions.
Several cloned animals have died prematurely from infections and other complications.
The same problems would be expected in human cloning. In addition, scientists do not
know how cloning could impact mental development. While factors such as intellect and
mood may not be as important for a cow or a mouse, they are crucial for the development
of healthy humans. With so many unknowns concerning reproductive cloning, the
attempt to clone humans at this time is considered potentially dangerous and ethically
irresponsible. See the Cloning Ethics links below for more information about the human
cloning debate.