Genetic engineering


16 déc. 2012 (il y a 9 années et 1 mois)

683 vue(s)

Genetic Engineering
Prepared by:
Ballesteros, Jessica; Briones, Leizel; Canillas, Carmela;
Comple, Roselle; dela Cruz, Kwini; Endrano. Blessy; Garcia,
Jonah; Lirio, Riza; Lugo, Lucila; Magpantay, Janssen
What is Genetic

Genetic engineering
, also
genetic modification
, is the
direct human manipulation of an 
 material in a way
that does not occur under 

Who would have thought that a tomato could
possess characteristics of a fish? What about a
plant possessing characteristics of a firefly; or a
pig with human traits? These things may sound
like science experiments gone wrong, but in
truth, these are products of experiments that
went well. The fish-like tomato and others are
results of genetic modification or genetic
manipulation, which are more commonly known
as genetic engineering.

Genetic engineering is the process of taking
genes and segments of DNA from one species
and putting them into another species, thus
breaking the species barrier and artificially
modifying the DNA of various species.

These changes in DNA result in an alteration of
reproductive and hereditary processes of the
organisms since the process is irreversible and
the organism's offspring will also possess this
unique DNA.

The Process of
Genetic Engineering

It is important first to understand the structure of
deoxyribonucleic acid, or DNA. Within its chemical
structure. DNA:

stores the information that determines an
organism's hereditary or genetic properties.

made up of a linked series of units called
nucleotides (Blaese), Different nucleotide
sequences determine different genes genetic
information. Genetic engineering is based on this
genetic information.
Isolating the Gene

First, the gene to be inserted into the genetically modified organism
must be chosen and isolated. Presently, most genes transferred
into plants provide protection against insects or tolerance to
herbicides. In animals the majority of genes used are growth
hormone genes.

Once chosen the genes must be isolated. This
typically involves multiplying the gene using polymerase chain
reaction (PCR). If the chosen gene or the donor
organism's genome has been well studied it may be present in
a genetic library. If the DNA sequence is known, but no copies of
the gene are available, it can be artificially synthesized. Once
isolated, the gene is inserted into a bacterial plasmid.

The gene to be inserted into the genetically modified organism must
be combined with other genetic elements in order for it to work
properly. The gene can also be modified at this stage for better
expression or effectiveness. As well as the gene to be inserted
most constructs contain a promoter and terminator region as well as
a selectable marker gene. The promoter region initiates transcription
of the gene and can be used to control the location and level of gene
expression, while the terminator region ends transcription. The
selectable marker, which in most cases confers antibiotic resistance to
the organism it is expressed in, is needed to determine which cells are
transformed with the new gene. The constructs are made
using recombinant DNA techniques, such as restriction
digests, ligations and molecular cloning.

Gene Targeting

The most common form of genetic engineering involves inserting new
genetic material randomly within the host genome. Other techniques
allow new genetic material to be inserted at a specific location in the host
genome or generate mutations at desired genomic loci capable of
knocking out endogenous genes. The technique of gene
targeting uses homologous recombination to target desired changes to a
specific endogenous gene. This tends to occur at a relatively low
frequency in plants and animals and generally requires the use
of selectable markers. The frequency of gene targeting can be greatly
enhanced with the use of engineered nucleases such as zinc finger
nucleases, engineered homing end nucleases, or nucleases created
from TAL effectors. In addition to enhancing gene targeting, engineered
nucleases can also be used to introduce mutations at endogenous genes
that generate a gene knockout.

About 1% of bacteria are naturally able to take up foreign
DNA but it can also be induced in other bacteria. Stressing the
bacteria for example, with a heat shock or an electric shock,
can make the cell membrane permeable to DNA that may
then incorporate into their genome or exist as
extrachromosomal DNA. DNA is generally inserted into animal
cells using microinjection, where it can be injected through
the cells nuclear envelope directly into the nucleus or through
the use of viral vectors. In plants the DNA is generally inserted
-mediated recombination or biolistics.

Not all the organism's cells will be transformed with the new
genetic material; in most cases a selectable marker is used to
differentiate transformed from untransformed cells. If a cell has
been successfully transformed with the DNA it will also contain
the marker gene. By growing the cells in the presence of an
antibiotic or chemical that selects or marks the cells expressing
that gene it is possible to separate the transgenic events from
the non-transgenic. Another method of screening involves using
a DNA probe that will only stick to the inserted gene. A number
of strategies have been developed that can remove the
selectable marker from the mature transgenic plant.

As often only a single cell is transformed with genetic material the
organism must be regrown from that single cell. As bacteria consist
of a single cell and reproduce clonally regeneration is not
necessary. In plants this is accomplished through the use of tissue
culture. Each plant species has different requirements for successful
regeneration through tissue culture. If successful an adult plant is
produced that contains the transgene in every cell. In animals it is
necessary to ensure that the inserted DNA is present in
the embryonic stem cells. When the offspring is produced they can
be screened for the presence of the gene. All offspring from the first
generation will be heterozygous for the inserted gene and must be
mated together to produce a homozygous animal.

Genetic manipulation is carried out through a process
known as recombinant-DNA formation, or gene splicing.
This procedure behind genetic engineering is one whereby
segments of genetic material from one organism are
transferred to another. The basis of the technique lies in
the use of restriction enzymes that split DNA strands
wherever certain desired secjuences of nucleotides, or
specific genes, occur. This desired segment of DNA is
referred to as donor DNA. The process of gene splicing
results in a series of fragments of DNA, each of which
express the same desired gene that can then combine with

Plasmids are small, circular molecules of DNA that are found in many
bacteria. The bacteria act as vectors in the process of genetic engineering.
The desired gene cannot be directly inserted into the recipient organism,
or host, therefore there must be an organism that can carry the donor
DNA into the host. Plasmid DNA is isolated from bacteria and its circular
structure is broken by restriction enzymes. The desired donor DNA is then
inserted in the plasmid, and the circle is resealed by ligases, which are
enzymes that repair breaks in DNA strands. This reconstructed plasmid,
which contains an extra gene, can be replaced in the bacteria, where it is
cloned, or duplicated, in large numbers. The combined vector and donor
DNA fragment constitute the recombinant-DNA molecule. Once inside a
host cell, this molecule is replicated along with the host's DNA during cell
division. These divisions produce a clone of identical cells, each having a
copy of the recombinant-DNA molecule and thus permanently changing
the genetic makeup of the host organism. Genetic engineering has been
The Many Uses of
Genetic Engineering

Are there any benefits that genetic engineering could bring to
humankind? Actually, there are many. By performing genetic
engineering, scientists can obtain knowledge about genetic
mechanisms. For example, they may be able to uncover some
secrets of genetic mapping. Genetic mapping is the
identification of individual genes for various functions. If
scientists are rising restriction enzymes to splice certain genes,
they must be able to identify the genes. Thus, genetic
engineering helps to identify certain nucleotide sequences, and
to use various restriction enzymes to "read" the sequences. For
example, if it appears that a single gene is responsible for a
certain function, the recombinant-DNA process may tell us
otherwise that two multiple genes, or even other factors are
responsible for the specific function.

Genetic manipulation is most commonly used
to transfer desirable qualities from one
organism to another to improve the ability of
other species to serve humankind. Many
examples of this lie in the use of genetic
engineering to solve many problems with
regards to food production and agriculture,
waste disposal and industry, as well as disease
and medicine. The processes are also used for
examining evolutionary processes.
Food Production and

Scientists have also developed transgenic bacteria that
protect strawberry plants from injury by frost. The bacteria
commonly found on strawberry plants secrete a protein
that initiates the formation of ice crystals when the
temperature falls to freezing. In the genetically modified
bacteria, the gene that codes for the protein has been
deleted. In the absence of the protein, ice formation does
not occur until the temperature falls well below the
freezing point. Normally, such a deep drop in the
temperature does not occur until after the harvest period
has ended. The first field test of these genetically modified
bacteria was conducted in 1987, on a plot of strawberry
plants, and similar experiments on potatoes showed that
the gene-spliced bacteria were effective in establishing
themselves on the plants and, later in the season, in
preventing ice formation during periods of light frost.
Genetic engineering has been used in plants as well as
in animals. In the livestock industry, for example, large
amounts of a growth hormone found in cows have
been obtained from genetically engineered bacteria.
When treated with this hormone, dairy cows produce
more milk, and beef cattle have leaner meat. Similarly,
a genetically engineered pig hormone causes hogs to
grow faster and decreases fat content in pork.
Waste Disposal and

Gene transfers also have been applied in the management of industrial
wastes. Genetically altered bacteria can be used to decompose many
forms of garbage and to break down petroleum products. For
example, an 'oil-eating "nonnatural manmade microorganism" exists,
and is used for cleaning up oil spills. Recombinant-DNA technology also
can be used to monitor the breakdown of pollutants. For example,
naphthalene, an environmental pollutant present in artificially
manufactured soils, can be broken down by the
Pseudomonas fluorescens
. To monitor this process, scientists
transferred a lightproducing enzyme called luciferase, found in the
Vibrio fischeri
, to the 
Pseudornonas fluorescens
The genetically altered 
Pseudomonas fluorescens
 bacterium produces
light in proportion to the amount of its activity in breaking down the
naphthalene, thus providing a way to monitor the efficiency of the
Disease and Medicine

Genetic engineering has been used in the field
of medicine for many purposes regarding the
control and improvement of health. The
process has been used to correct inherited
genetic defects causing disease (gene
therapy), to counter effects of genetic
mutations, to produce various
pharmaceutical products.

Gene therapy is the use of genetic engineering techniques in the
treatment of a genetic disorder or chronic disease. In 1990, a four-
year-old girl received genie therapy treatment for adenosine
deaminase (ADA) deficiency, an ordinarily fatal inherited disease
of the immune system. Because of this genetic defect, the girl was
susceptible to recurrent life-threatening infections. Doctors
removed white blood cells from the child's body, let the cells grow
in the lab, used a genetically modified virus to carry a normal
ADA gene into her immune cells, and then infused the genetically
modified blood cells back into the patient's bloodstream. The
inserted ADA gene then programmed the cells to produce the
missing ADA enzyme, which led to normal immune function iii
those cells. This treatment temporarily helped her to develop
resistance to infection, and must be repeated periodically .

Genetic engineering has also contributed
several pharmaceutical products (besides
vaccinations). Recombinant-DNA procedures
involving bacteria and donor DNA fragments
have led to the increased availability of such
medically important substances as insulin,
interferon, and growth hormone. These
substances were previously available only in
limited quantities from their primary sources.

Surprisingly, genetic engineering can also be used to
uncover the past. Recombinant-DNA procedures have
been used to study the genes of extinct animals. A
zebra-like animal called the quagga, for example,
became extinct in the '1 9th century, but some quagga
skins with underlying muscle tissues have been salt-
preserved in museums. Enzymes were used to release
DNA from these muscle cells, yielding DNA fragments
representing parts of different genes. These fragments
were transferred to the plasmids of bacteria, where
they were replicated along with the bacterial DNA.

They were then retrieved, analyzed, and
compared to corresponding DNA segments of
closely related living animals, revealing that the
quagga DNA differs from its zebra counterpart by
about 5 percent. This amount of difference
indicates that the quagga and zebra shared a
common ancestor. With appropriate
modifications, it should be possible to use this
technique to study genes from the bones and
teeth of long-extinct animals, providing new
insights into the evolutionary process.
The Dangers of Genetic

Even though it may seem as if genetic engineering has
so many positive aspects, there are just as many
negatives to counter. Genetic engineering is really a test
tube science which may be prematurely applied. A gene
studied under a closed system, a test tube with no
outside influence on the conditions of the experiment,
can only give results about what it does and how it
behaves in that particular system. The experiment
cannot tell what the role and behavior of donor DNA
will be once it's in the host cell, which is likely to be a
totally unrelated species that may be very different
from the experimental environment .

The insertion of a foreign gene might trigger new cellular
activities or interrupt current ones. For example, genes
can normally be exchanged between different species,
but the frequency of these natural transfers is limited by
their defense(immune) systems. The immune system
serves to prevent invasion by harmful foreign genes,
viruses, and other substances, so that particular species is
able to maintain its characteristic traits and normal
metabolism. Genetic engineering, may, in turn, disrupt
and weaken the immune systems by introducing foreign
substances into organisms that they won't be able to
fight. No one really knows the overall effect of this.

Foreign genes trigger new cellular activities in the
form of resistance. The vectors used in the genetic
engineering process are often resistant to many
drugs such as antibiotics. Injecting a drug-resisting
vector into a new organism will result in a drug-
resistant host organism. The resistance may not
necessarily be only to drugs, as is the case with
frost-resistant plants. Since genetic engineering is
irreversible, this method allows these altered
organisms to become widespread in nature .

Creating organisms that are resistant to anything they weren't
initially unaffected by disturbs the evolutionary process of natural
selection, or survival of the fittest. Putting such a desirable gene into
an organism may give them an edge over another that would not
normally exist. This whole idea of meddling with nature raises a
question of religion and ethics. What about "God;" Do we have the
right to be playing the role of a higher being? In fact, genetic
engineering raises countless more unanswered questions. Should
animals be used in research? Do animals have "rights", as we think
of "human rights?" How does genetic engineering of food affect
religious and other groups with strong dietary laws, such as
vegetarians? How great are the potential risks involved in releasing
genetically modified organisms into the biosphere without knowing
all the possible consequences?

New toxins and allergens in foods as well as other
damaging effects on health caused by unnatural
The process of genetic engineering can thus
introduce dangerous new allergens and toxins into
foods that were previously naturally safe. Already,
one genetically engineered soybean was found to
cause serious allergic reactions, and bacteria
genetically engineered to produce large amounts
of the food supplement tryptophan have
produced toxic contaminants that have killed 37
people and permanently disabled 1,500 more.

The disturbance of ecological balance and the spread of
diseases across species barriers:
 When genetic engineers
insert a new gene into any organism, there are "position
effects" which can lead to unpredictable changes in the
pattern of genetic function. The protein product of the
inserted gene may carry out unexpected reactions and
produce potentially toxic products. There is also serious
concern about the dangers of using genetically
engineered viruses as vectors in the generation of
transgenic plants and animals. This could destabilize the
genome, and also possibly create new viruses, and thus
dangerous new diseases.

Unnatural loss of bio-diversity in crops:
companies claim that their manipulations are similar to
natural genetic changes or traditional breeding techniques.
However, the cross-species transfers being made, such as
between fish and tomatoes, or between other unrelated
species, would not happen in nature and may create new
toxins, diseases and weaknesses. Also consider the fact that
organisms are "sharing" characteristics that are supposed to
be unique to them. , For example in the fish-like tomato, a
fish and a tomato are no longer unique. There is less
diversity since they are now more similar, though
unnaturally, than they initially were.

The creation of herbicide-resistant weeds,
resulting in increased pollution of food and
water supply:
 More than 50% of the crops
developed by biotechnology companies have
been engineered to be resistant to herbicides.
Use of herbicide-resistant crops will lead to a
threefold increase in the use of herbicides,
resulting in even greater pollution of our food
and water with toxins.

Unexpected characteristics may appear
in genetically altered organisms:
batch of genetically engineered young
salmon were pale green instead of the
normal brown color of young salmon
and rather than turning pink on
maturation, they remained green.

Artificially induced characteristics and
inevitable side effects will be passed on to all
subsequent generations and to other related
organisms. Once released, they can never be
recalled or contained. The consequences of
this are incalculable. Even when genetically
engineered fish have appeared normal, their
descendants have been born with deformities
such as grotesquely deformed heads and gill
flaps, and change of color.