Human Cloning and Genetic
Modification-
The Basic Science You Need to Know
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I. GENES
Genes are strings of chemicals that help create the proteins that make
up your body. Genes are found in long coiled chains called chromosomes.
They are located in the nuclei of the cells in your body:
II. "THREE WAYS TO MAKE AN EMBRYO"
In sexual reproduction a child gets half its genes from its mother (in
her egg) and half from its father (in his sperm):
Cloning is an asexual form of reproduction. All the child's genes
would come from a body cell of a single
individual:
Who is the clonal child's genetic mother or father? As we understand
those terms, a clonal child wouldn't have a genetic mother or father,
it would have a single 'nuclear donor.' If a man cloned himself, would
the child be that man's son or his twin brother? It would be neither,
it would be a new category of biological relationship: his clone.
III. STEM CELLS
Stem cells are primordial cells capable of developing into a variety
of types of cells. Some stem cells are found in the adult body. Others
are found in very early embryos. These stem cells can be cultured in
petri dishes and potentially used to generate "therapeutic tissues"
or "spare organs":
Many people support the use of stem cells of both types for such therapeutic
purposes. Many others support the use of adult stem cells
for this purpose but oppose the use of embryonic stem
cells, because they oppose the destruction or manipulation of human
embryos.
IV. HUMAN CLONING: A CRITICAL DISTINCTION BETWEEN TWO APPLICATIONS
1. Reproductive cloning uses the cloning procedure to
produce a clonal embryo which is implanted in a woman's womb with intent
to create a fully formed living child--a clone-as shown in diagram 3
above..
2. Therapeutic cloning uses the cloning procedure to
produce a clonal embryo, but instead of being implanted in a womb and
brought to term it is used to generate stem cells, as shown in diagram
4 above.
The purpose of using clonal embryos to generate stem cells is to allow
creation of tissues or organs that the clonal donor can use without
having these tissues or organs rejected by their body's immune system.
Most people oppose reproductive cloning. Some people oppose reproductive
cloning but support therapeutic cloning. Others oppose therapeutic cloning
as well as reproductive cloning, either because they are opposed to
the destruction of embryos as a matter of principle, or because they
feel the acceptance of therapeutic cloning will set us on a slippery
slope to the acceptance of reproductive cloning and human genetic manipulation.
It is possible to support stem cell research and still oppose research
involving therapeutic cloning.
V. HUMAN GENETIC ENGINEERING
Human genetic engineering means changing the genes in a living human
cell. Suppose you had a lung disease caused by defective genes in your
lung cells. If there was a way to fix those genes, you might be cured.
Scientists change the genes in living cells by putting the desired
"new" gene into a little virus-like organism which is allowed to get
into your cells and which inserts the new gene into the cell along with
the "old" genes:
VI. HUMAN GENETIC ENGINEERING: A CRITICAL DISTINCTION BETWEEN TWO
APPLICATIONS
1. "Somatic" genetic engineering is genetic engineering
that targets the genes in specific organs and tissues of the body of
a single existing person without affecting genes in their eggs or sperm.
Somatic gene transfer experiments are currently undergoing clinical
trials, with mixed results to date. But they may someday be effective.
Diagram 5 above shows how somatic genetic engineering works.
2. "Germline" genetic engineering is genetic engineering
that targets the genes in eggs, sperm, or very early embryos. The alterations
affect every cell in the body of the resulting individual, and are passed
on to all future generations. Germline engineering is banned in many
countries but not in the U.S. Diagram 5 shows how germline genetic engineering
works.
[note: The term "somatic" comes from
the Greek "soma" for "body." The term "germline" refers to the "germ"
or "germinal" cells, the eggs and sperm.
VIII. PRE-IMPLANTATION GENETIC DIAGNOSIS AND SELECTION (PDS)
Many people assume that germline engineering is necessary to allow couples
at risk of passing on a genetic disease to avoid doing so. This is not
so. Procedures already exist that make this possible, including adoption
and gamete and embryo donation. In addition the alternative of pre-implantation
diagnosis and selection allows couples to have a child that
is fully genetically related to both of them and which does not carry
the genetic disease about which they are concerned.
The PDS procedure begins in the same way that germline engineering
would, with an IVF procedure, but instead of seeking to change
the genes in unhealthy embryos it simply selects the healthy
embryos themselves for implantation in the mother:
This technique is more straightforward than germline genetic manipulation,
and does not open the door to an out-of-control techno-eugenic human
future. The only situation in which germline engineering would be required
over pre-implantation selection is one in which a couple would like
to endow their child with genes that neither member of the couple possesses.
This is the "enhancement" scenario, which we believe would lead to a
dystopic human future if it were allowed. PDS, on the other hand, would
have only a minimal effect on the human genome, even if it were widely
used, because the procedure selects from the range of existing human
traits. But engineering the genes by means of germline
modification would allow novel forms of human life to be created within
one generation.
While pre-implantation diagnosis and selection can be used for the
acceptable reasons of preventing genetic disease, it could also be used
in ways that societies might find unacceptable, eg., to select for cosmetic,
behavioral, or other non-disease traits. Societies have the right and
responsibility to decide which uses of such screening technologies should
be allowed and which should be banned.
Click
here for a printable PDF version of this brochure
ARHP's
Genetic Engineering Resource Center
Read
a Transcript from ARHP's Recent Debate on Genetic Engineering
Many sections of this ARHP educational tool are taken
from Human Cloning and Genetic Modification: The Basic Science You
Need to Know' by the Center for Genetics and Society, with their
permission.
Center for Genetics and Society
436 14th Street, Suite 1302, Oakland, CA 94612
tel: 510-625-0819
fax: 510-625-0874
e-mail: info@genetics-and-society.org
Website: www.genetics-and-society.org
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