From Wikipedia,
the free encyclopedia.
A genetically modified
organism is an organism whose
genetic material has been
altered using techniques generally
known as "recombinant DNA
technology". Recombinant DNA
technology is the ability to
combine DNA molecules from
different sources into the one
molecule in a test tube. The first
GMO was created in 1973 by Stanley
Cohen and Herbet Boyer [[1]].
The term generally does NOT
cover organsims who's genetic
makeup have been altered by
conventional cross breeding or by
"mutagenesis" breeding as these
methods pre-date the discovery of
the recombinant DNA techniques.
Examples of GMOs are diverse, and
include transgenic experimental
animals such as
mice, transgenic plants, or
various microscopic organisms
altered for the purposes of
genetic research or for the
production of pharmaceuticals.
"Genetically modified organism"
does not necessarily imply (but
does include) transgenic
substitution of genes from another
species, although research is
actively being conducted in this
field. For example, genes for
fluorescent proteins can be
co-expressed with complex proteins
in cultured cells to facilitate
study by
biologists, and modified
organisms are of great use in
researching the mechanisms of
cancer and other
diseases.
History
In mid-1974, very soon after
the first GMO was created,
scientists called for and observed
a voluntary moratorium on certain
recombinant DNA experiments. One
goal of the moratorium was to
provide time for a conference that
would evaluate the state of the
new technology and the risks, if
any, associated with it. That
conference was held in February of
1975 at the Asilomar Conference
Center on California's Monterey
peninsula in the USA. The
conference concluded that
recombinant DNA research should
proceed but under strict
guidelines. Such guidelines were
subsequently promulgated by the
USA's National Institutes of
Health and by comparable bodies in
other countries. These guidelines
form the basis upon which GMOs are
regulated to this day. [[2]]
Terminology
Gene splicing - 1. [n]
the technology of splicing
together DNA fragments from more
than one organism and thus
preparing a "recombinant" DNA
molecule in a test tube. This is
achieved by cutting up DNA
molecules with
restriction enzymes and
splicing these fragments together
using
DNA ligase.
Transgenic - an organism
that contains DNA sequences from a
foreign organism integrated into
its own genome ; literaly across
gene. An example is any animal
besides jelly fish that expresses
the green flouresence protein
(glow-in-the-dark-when-exposed-to-a-blacklight
gene) such as mice or fish because
that gene originated from jelly
fish.
knock outs - knock out
organism are organism in which a
specific gene has been functionaly
destroyed or "knocked out." They
are used extensively in disease
research with model organisms. For
example, when investigating the
cause of cystic fibrosis,
researchers identified the CFTR
gene as a very likely candidate
for the disease, found the mouse
equivalent , bred a mouse with
this gene "knocked out", and noted
that the knockout mouse also had
cystic fibrosis.
vector - means by which
new DNA is introduced into the
receiving host. Vectors can be
anything from small circular
pieces of DNA (plasmids),
to various viruses that can carry
and transmit genetic information.
Methods of genetic
modification
Genetic modification of
bacteria
Three processes are known by
which the genetic composition of
bacteria can be altered:
transformation is a process by
which some bacteria are naturally
capable of taking up
DNA to acquire new genetic
traits. This phenomenon was
discovered by
Frederick Griffith in
1928, although the fact that
it was specifically DNA molecules
that carried the genetic
information was not proven until
1944. Bacteria that are
competent to undergo
transformation are frequently used
in
molecular biology.
Transformation does not normally
integrate new DNA into the
bacterial
chromosome. Instead, it
remains on a
plasmid.
- In conjugation, DNA is
transferred from one bacterium
to another via a temporary
connecting tube of protien
called a pilus (a process
analogous to but biologically
distinct from mating).
Conjugation is not widely used
for the artificial genetic
modification of bacteria.
-
Transduction refers to the
introduction of new DNA into a
bacterial cell by a
bacteriophage (a
virus that infects
bacteria).
Genetic modification of plants
- See main article
Transgenic plants.
The principal technique for the
genetic modification of
plants is based on a natural
ability of the bacterium
Agrobacterium tumefaciens.
This bacterium infects plants and
causes a tumor-like growth termed
a
crown gall. A. tumefaciens
contains a
plasmid (a circular piece of
DNA) that transfers from the
bacteria into the infected plant
and integrates into the plant's
genome. The transferred genes
cause the plant to form the gall,
which houses the bacteria and
produces nutrients that support
the bacteria's growth. A number of
scientists contributed to this
discovery throughout the late
1960s and the
1970s, with key discoveries by
Jeff Schell,
Marc Van Montagu,
Georges Morel,
Mary-Dell Chilton and
Jacques Tempé. By
1983
biotechnology had reached the
point where it was possible to
insert additional genes of
interest into A. tumefaciens
and thus transfer those genes into
plants. This process is commonly
used to create
transgenic crop plants for
agricultural purposes. Another
widely used process to create
transgenic crops is biolistic
method (gene
gun). Biolistic method was
also used for the creation of two
most common transgenic crops -
RoundUp ready soybean and
Bt-corn.
Genetic modification of
animals
Like bacteria and plants,
animals can be genetically
modified by viral infection.
However, the genetic modification
occurs only in those cells that
become infected, and in most cases
these cells are eventually
eliminated by the
immune system. In some cases
it is possible to use the
gene-transferring ability of
viruses for
gene therapy, i.e. to correct
diseases caused by defective genes
by supplying a normal copy of the
genes. Permanent genetic
modification of whole animals can
be accomplished in
mice. The process begins by
first genetically modifying a
mouse
embryonic stem cell. This is
normally done by physically
introducing into the cell a
plasmid that can integrate into
the genome by a process known as
transfection [[3]].
Durring transfection the DNA
itergrates into the animal genome
using non-homologous
recombination. This altered cell
is implanted into a
blastocyst (an early embryo),
which is then implanted into the
uterus of a
female mouse. A pup born from
this blastocyst will be a
chimera containing some cells
derived from the unmodified cells
of the blastocyst and some derived
from the modified stem cell. By
selecting mice whose germ cells
(sperm or egg producing cells)
developed from the modified cell
and interbreeding them, pups that
contain the genetic modification
in all of their cells will be
born.
There has also been the
genetically manipulated bull
Herman with 55 offspring. A human
gene was built into his genetic
code while in an early embryonic
stage in 1990. As a result, milk
from his female descendants
contained the human protein
lactoferrine, that can be used as
medicine, but it was present at
such low levels that it was not
profitable to extract them.
Insects can be genetically
modified by injecting them with
artificial
transposons and a source of
transposase. The transposon,
which can include new genes, is
then integrated into the genome.
Such insertions are unstable and
can 'jump-out' in the presence of
transposase.
Controversies over genetic
modification
See also
Genetically modified food and
Transgenic plants
Genetic modification (GM) is
the subject of controversy in its
own right
[4]. Some see the science
itself as intolerable meddling
with "natural" order, despite
known examples of natural genetic
crossings occurring throughout
history. While some would like to
see it banned, others push simply
for required labeling of
genetically modified food.
Other controversies include the
definition of patent and property
pertaining to products of genetic
engineering and the possibility of
unforeseen global side effects as
a result of modified organisms
proliferating. The basic ethical
issues involved in genetic
research are discussed in the
article on
genetic engineering.
In 2004,
Mendocino County, California
became the first county in the
United States to ban the
production of GMOs. The measure
passed with a 57% majority. In
2005, a
standing committee of the
government of
Prince Edward Island in
Canada began work to assess a
proposal to ban the production of
GMOs in the province. This is a
largely symbolic and empty gesture
as PEI has already banned gmo
potatoes, which acount for most of
its crop. The Californian counties
of Trinity and Marin counties have
also imposed bans on GM crops,
while ordinances to do so were
unsuccessful in Butte, San Luis
Obispo and Humboldt counties.
Supervisors in the ag-rich
counties of Fresno, Kern, King,
Solano, Sutter and Tulare have
passed resolutions supporting the
practice [[5]].
Currently, there is little
international consensus regarding
the acceptability and effective
role of modified "complete"
organisms such as plants or
animals. A great deal of the
modern research that is
illuminating complex biochemical
processes and disease mechanisms
makes vast use of genetic
engineering.
The practice of genetic
modification as a scientific
technique is not restricted in the
United States. Individual
genetically modified crops (such
as soybeans) are subject to
intense study before being brought
to market and are common in the
United States, but estimates of
their market saturation vary
widely. Some countries in
Europe have taken the opposite
position, stating that genetic
modification has not been proven
safe, and therefore that they will
not accept
genetically modified food from
the United States or any other
country. This issue has been
brought before the
World Trade Organization,
which determined that not allowing
modified food into the country
creates an unnecessary obstacle to
international trade. Consequently,
genetic modification within
agriculture is an issue of
some strong debate in the United
States, the
European Union, and some other
countries.
Some critics have raised the
concern that conventionally bred
crop plants can be
cross-pollinated (bred) from the
pollen of modified plants. Pollen
can be dispersed over large areas
by wind, animals, and insects.
Recent research has lent support
to the concern when modified genes
were found in normal plants up to
21 km (13 miles) away from the
source, and also within close
relatives of the original plants.
GM proponents point out that
outcrossing, as this proces is
known as, is not new. The same
thing happens with any new crop
variety - newly introduced traits
can potentially cross out into
neighbouring crop plants of the
same species and to closely
related wild relatives of crop
plants. Defenders of GM technology
point out that each GM crop is
assessed on a case by case basis
to determine if there is any risk
associated with the out crossing
of the GM trait into wild plant
populations. The fact that a GM
plant may outcross with a related
wild relative is not, in itself, a
risk unless such an occurance has
consequences. If, for example, a
herbicide resistance trait was to
cross into a wild relative of a
crop plant it can be predicted
that this would not have any
concequences except in areas where
herbicides are sprayed - eg a
farm. In such a setting the farmer
can manage this risk by rotating
herbicides.
Naturally-occurring genetic
crossings
In nature, genes have crossed
species and genera barriers in the
past. Today's modern red wheat
variety is the result of two
natural crossings made long ago.
It is made up of three groups of
seven chromosomes. Each of those
three groups came from a different
wild wheat grass. First, two of
the grasses became crossed,
creating the
durum wheats, which were the
commercial grains of the first
civilizations up through the
Roman Republic. Subsequently,
that 14-chromosome durum wheat
became crossed with another wild
grass to create what became modern
red wheat at the time of the
Roman Empire.
However, what distiguishes
genetic modification is that it
recognises no boundaries. Thus it
becomes possible to splice animal
genes into plants, and vica versa,
which would be impossible
otherwise.
