Genetically Engineering Plants - Faperta


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

362 vue(s)

Genetically Engineering

Riyanda N G (10198)

Vina E A (10221)

Arini N (10268)

Suluh N (10302)

Overview of The Process

There are five major steps involved in genetically engineering
plants. These are DNA isolation, single gene cloning, gene
designing, cell transformation, and backcross breeding.

DNA is extracted from an organism that has the desired trait.

The desired gene is located and copied.

The gene is inserted into a single plant cell using a
transformation method. If the transgene successfully lands in
the cells nucleus and is incorporated into one of the
chromosomes, then the trait that it codes for will be expressed
in the cell's offspring.

The cell multiplies and grows a new plant that contains the
transgene in all of its cells.

Through backcross breeding the transgenic plant is crossed
with a plant from a high yielding line. The resulting hybrids are
the genetically modified plants that can enter the marketplace.

DNA Isolation

Inside all plants cells
is a nucleus, the
"brain" of the cell. The
nucleus contains all of
the information the
cell needs. This
information is stored
on chromosomes,
made up of tightly
spiraled DNA.

DNA is composed of four different nucleotides:
adenine (A), guanine (G), thymine (T), and
cytosine (C). These nucleotides make up the
genetic language of life. The order of the
nucleotides encodes all of the cell's information.

A set of nucleotides that code for a particular
protein is called a gene, and each chromosome
contains thousands of genes. Since the proteins
a cell produces are responsible for its specific
traits, by changing the genes of an organism you
can change its proteins, and therefore its traits.

Cloning Genes

Gene cloning is used to
locate and copy a
specific gene from the
entire DNA of an
organism. For
example, suppose the
red gene in this
bacterium needs to
be extracted from the
rest of the DNA in
order to be added to a

The DNA is removed
from bacteria cells
and isolated in a test
tube. A restriction
enzyme is added to
the isolated DNA, and
cuts the extracted
bacterial DNA into
sized pieces.

In another test tube,
extracted bacterial
plasmids are cut
using the same
restriction enzyme.
The cut plasmids are
mixed with the gene
sized pieces of DNA.

The two combine to
form recombinant
plasmids. Some of
the plasmids will
recombine with
themselves without
picking up the
bacterial DNA. These
will be useless. Other
plasmids will contain
the gene of interest

Designing Genes

Each gene has three distinct regions



Signals how much protein to
produce and when it should be made.

Coding Region


Encodes which protein to
produce. In order, codons (sets of three
nucleotides) are read by the cell, specifying the
next amino acid that must be made and added
to the chain.

Termination Sequence


Signals the end of a
gene, preventing the cell from combining two or
more coding regions.

Genetic engineers can alter or replace one
or more of the three regions to design a
gene so that it will be expressed in a
specific way in a plant cell. Here is an
example of different genetic modifications
that can be achieved by manipulating the
gene sequence.

Combining 35S with Bt. CRYIA and inserting this gene in
corn will make all parts of the plant poisonous to the corn
borer. Combining PEP Carboxylase with Bt. CRYIA will
produce a plant that is poisons to the corn borer only if
the pest eats the green parts of the plant. Corn stalks,
silks, and late season plants that have slowed their
photosynthesis will remain edible to the borer.

The same holds for the Round Up Resistance coding
region. Combining it with 35S will produce a plant that is
completely immune to Roundup.


There are a variety of methods available
for moving genes into recepient cells. The
oldest method involves

Newer methods involve
electro and chemical poration
, and

Recombinant DNA

It is biological organisms like plasmids or viruses carry foreign
genes into cells.

Plasmids are small, circular pieces of DNA found in bacteria cells
that are capable of crossing membranes. Plasmids can be removed
from bacteria. Circular plasmids are cleaved and new genes are
inserted. The modified plasmid can then crosses cell borders and
combine with the recepient cell's DNA along with the additional

Viruses, infectious particles that contain genetic material, are also
used to transfer genes to a cell's DNA. Desired genes can be added
to a virus. The virus can then carry these genes into a recipient cell
in the process of infecting that cell. The virus is disabled so that
while it can carry a new gene into a cell, it cannot redirect the cell's
genetic machines to replicate the virus and kill the cell.


It is simply injecting genetic material
containing the new gene into the recipient

Microinjection is not well understood.
Somehow the injected genes find the host
cell genes and incorporate themselves into
them. In larger cells, like many plant and
animal cells, microinjection can be
performed with a fine
tipped glass needle.


and Chemical Poration

It is creating holes in the cell membrane to
allow new genes to enter.

Pores are created either by soaking the
cells in chemicals that open up holes in
cell membranes, or by running weak
electric currents through the cells, also to
open pores in the membrane.


It is Projectile method utilizing metal slivers to
deliver genes to the interior of the cell.

Very small slivers of metal, much smaller than
the cell diameter, are coated in genetic material.
The coated slivers are propelled into the cell
using a shot gun. A metal plate placed before
the cells stops the shell cartridge, but allows the
slivers to pass through and into the cells on the
other side. Once inside the cell, the genetic
material is taken to the nucleus and incorporated
into the recipient's DNA

Plant Breeding

After obtaining a transgenic event, the genetic
engineer hands the seeds over to the plant

Lines that survive transformation and tissue
culture well are typically lower yielding than
current elite lines. To make these transgenic
lines marketable, plant breeders must use
breeding techniques to transfer the transgene
into a high yielding elite line.

First, the breeder obtains an
inbred line by self
pollinating the transgenic line
. Each plant cell
in the transgenic inbred line now contains two
copies of the gene.

The transgenic seeds produced are planted
along with seeds from an elite inbred.

Due to a lack of hybrid vigor, both of the inbred
plants that grow from these seeds will be smaller
than current hybrids.

When the plants reach the proper stage, they
are cross

The seed from this crop, the
F1 seed
, is
harvested. All of the offspring have
one copy of
the transgene
, as well as
50% elite and 50%


The F1 seed is planted near another elite inbred
seed. The plants grow. Due to hybrid vigor, the
F1 plant is larger than the elite inbred, but it still
contains many undesirable genes.

The F1 plant is mated back to the elite inbred.
This process is known as

This seed, the
backcross 1 (BC1)

generation is harvested. The plants that
grow from these seeds will have
75% elite
, and

will contain the

Again, BC1 plants are grown along with
elite inbreds. Those that express the
transgene are cross
pollinated with the
elite inbreds.

This process is continued until the plants
contain at least
98% of the elite genes

and the transgene
. This takes
5 to 6 generations

Has genetic engineering of foods
been done?

A FlavrSavr tomato,
engineered to be more

Peter Beyer demonstrating golden
rice, engineered to be more nutritious.