EMBRYO CLONING OF HUMANS:
(a.k.a. ARTIFICIAL TWINNING)
Embryo cloning topics covered
in this essay:
Cloning is the production of one or more individual plants or animals that are
genetically identical to another plant or animal.
Embryo cloning might be more accurately called "artificial twinning",
because it simulates the mechanism by which twins naturally develop. It involves removing one or more cells from an embryo and
encouraging the cell to develop into a separate embryo with the same
DNA as the original. It has been successfully carried out for years on
many species of animals. Some very limited experimentation has been done on human embryos.
Nature itself is the greatest cloning
agent. In about one of every 75 human conceptions, the fertilized ovum splits for some
unknown reason and produces monozygotic (identical) twins. Each has an genetic makeup
identical to the other. In cloning, this same operation is done intentionally in
Human embryo cloning starts with a standard in vitro fertilization procedure.
Sperm and an egg cell are mixed together on a glass dish. After conception, the zygote
(fertilized egg) is allowed to develop into a blastula (a hollow mass of cells). The
zygote divides first into two cells, then four, then eight... A chemical is added to the
dish to remove the "zona pellucida" covering. This material provides nutrients
to the cells to promote cell division. With the covering removed, the blastula is divided
into individual cells which are deposited on individual dishes. They are then coated with
an artificial zona pellucida and allowed to divide and develop. The experiment by Sillman
et al. showed that the best results could be obtained by interrupting the zygote at the
two cell stage. Many of these pairs of zygotes were each able to develop to the 32 cell stage,
but stalled at that point. They might well have had the potential to develop further and even mature
into a viable fetus, except that the original ovum was defective and would have died
anyway. For ethical reasons, the researchers had selected embryos which had no possibility of
ever maturing into fetuses, and thus becoming newborn babies.
Cloning of embryos
has been used in mice experiments since the late 1970's, and in animal breeding since the late 1980's. The procedure splits a single fertilized ovum into two or more clones, each of
which is then implanted into the womb of a receptive female.
However, research into cloning of human embryos has been restricted in the United
States and in some other countries. Pro-life groups which oppose free
access to abortion have had considerable political power. They were able to have all
human embryo research banned by the Regan and Bush Presidencies during most of the 1980's
and into the early 1990's. During the first few days of President Clinton's presidency,
the ban on public funding of human embryo and fetal research was lifted.
We may not know the individual or team who first performed cloning of human embryos.
The methods used have been understood for many years and actually used to clone embryos in
cattle and sheep. It is likely that someone had successfully used the method on a human embryo
in secret. The first publicly announced human cloning was done by Robert J. Stillman and
his team at the George Washington Medical Center in Washington D.C. They took 17
genetically flawed human embryos which would have died within days no matter how they were treated.
They were derived from an ovum that had been fertilized by two sperm. This resulted in an
extra set of chromosomes which doomed the ovum's future. None could have developed into a
fetus. These ovum were successfully split in 1994-OCT, each producing one or more clones.
The main motive of the experiment seems to have been to trigger public debate on the
ethics of human cloning.
Dr. Steven Muller headed a panel in the US whose mandate was to produce preliminary
cloning guidelines. These would be used by the Federal National Institutes of Health
to decide which cloning research to fund. The panel recommended that studies be normally
limited to the use of preexisting, spare embryos - those that developed during in vitro
fertilization procedures that had been performed to assist couples in conceiving.
Generally about 20 or 24 ova are fertilized during these procedures. Only three or four are
implanted in the woman. The
extra zygotes are either discarded or frozen for possible future use.
New embryos would only be prepared and used if needed for "compelling research."
They further recommended that any studies be normally terminated within 14 days of
conception. Some experiments might be authorized to continue until the 18th day, but no
further. At that gestational age, neural tube closure begins; this is the start of the
development of a nervous system. They recommended that certain procedures be banned,
including implanting human embryos in other species, implanting cloned embryos into
humans, the transfer of a nucleus from one embryo to another, and the use of embryos for
Cloning of animals seems to have a number of potentially positive
||Scientists are attempting to create transgenic pigs which have human genes. Their heart,
liver or kidneys might be useable as organ transplants in humans. This would save many
lives; thousands of people die each year waiting for available human organs. Once
achieved, transgenic animals could be cloned to produce as many organs as are needed.
||Experience gained in cloning may add to our understanding of genetics.
||Researchers have produced transgenic animals. These are genetically altered, typically
in order to produce human hormones or proteins in its milk. These materials can be
separated from the milk and used to heal humans. Cloning would produce as many genetically
altered animals as are needed. The alternative is to simply allow them to mate; this would
produce many offspring that had lost the inserted human gene and thus would be unable to
produce the medication.
Embryo cloning of humans: Some scientists believe that embryo cloning and
related research is moral and might eventually lead to very positive results:
||It might produce greater understanding of the causes of miscarriages; this might lead to
a treatment to prevent spontaneous abortions. This would be of immense help for women who
cannot bring a fetus to term.
||It might lead to an understanding of the mechanisms by which a morula (a mass of cells
that has developed from a blastula) attaches itself to the wall of the uterus. This might
generate new, effective contraceptives that exhibit very few side effects.
||The rapid growth of the human morula is similar to the rate at which cancer cells
propagate. Cancer researchers believe that if a method is found to stop the division of a
human ovum then a technique for terminating the growth of a cancer might be found.
||Parents who are known to be at risk of passing a genetic defect to a child could make
use of cloning. A fertilized ovum could be cloned, and the duplicate tested for the
disease or disorder. If the clone was free of genetic defects, then the other clone would
be as well. The latter could be implanted in the woman and allowed to mature to term.|
||In conventional in vitro fertilization, doctors attempt to start with many ova,
fertilize each with sperm and implant all of them in the woman's womb in the hope that one
will result in pregnancy. But some women can only supply a single egg; her
chances of becoming pregnant are slim. Through the use of
embryo cloning, that egg might be divisible into, say, 8 zygotes for implanting. The
chance of those women becoming pregnant would be much greater.|
||Cloning could produce a reservoir of "spare parts". Fertilized ova could be
cloned into multiple zygotes; one could be implanted in the woman and allowed to develop
into a normal baby; the other zygotes could be frozen for future use. In the event that
the child required a bone marrow transplant, one of the zygotes could be taken out of
storage, implanted, allowed to mature to a baby and then contribute some of its spare bone
marrow to its (earlier) identical twin. Bone marrow can be harvested from a person without
||A woman could prefer to have one set of identical twins, rather than go through two
separate pregnancies. She might prefer this for a number of reasons:
||to minimize disruption to her career.
||to make a normal vaginal delivery possible (twin fetuses are smaller than a single
fetus; delivery of a larger, single fetus might be impossible because of her shape.
||she might prefer to only have to endure the discomfort of a single pregnancy.
||she might wish to have children that could contribute a kidney to their sibling, if
Through embryo cloning, she could be assured that she would deliver identical twins.
Some individuals and groups have expressed concerns about adverse effects of embryo cloning
in humans, and question its morality:
||The genetic screening test described above could also be used to eliminate zygotes of a
particular gender, without requiring a later abortion.
||When the gene or genes that determine sexual orientation are located, cloning could also
be used to eliminate zygotes of a particular sexual orientation.
||A country might finance a program similar to that of Nazi Germany whereby humans were
bred to maximize certain traits. Once the "perfect human" was developed, embryo
cloning could be used to replicate that individual and conceivably produce unlimited
numbers of clones. The same approach could be used to create a genetic underclass for
exploitation: e.g. individuals with sub-normal intelligence and above normal strength.
||There is always the possibility of injuring or killing embryos. Most
pro-life supporters believe that an embryo is a human person. During
embryo cloning, they would be subjected to assault with the possibility
of being murdered. The embryos would be treated as a commodity to be
exploited, not as a person.
Dr. B. Benoit maintains a Web page "HUMAN CLONING AND RE-ENGINEERING"
that is dedicated to "the dissemination of information on human embryo cloning
research and related topics, with special attention dirrected [sic] to the moral
implications." See: http://cac.psu.edu/~gsg109/qs/emclone.html
Copyright ©1997 to 2001 incl. by Ontario Consultants on
Originally published: 1997-AUG-5
Extracted from the cloning menu on 2001-MAR-20
Last updated 2001-AUG-17
Author: B.A. Robinson