Genetically modified organization

Legal definition

Within the European Union, the Directive 2001/18/CE defines a GMO as follows:

A Organisme genetically modified is an organization (except for the human beings) whose genetic material was modified in a manner which cannot be carried out naturally by multiplication and/or recombination.

The Directive 2001/18/CE indicates that the techniques of genetic modification aimed in this definition are, inter alia:

1) techniques of recombination of the desoxyribonucleic Acid implying the formation of new combinations of genetic material by the insertion of molecules of Nucleic acid, produced any way out of an organization, inside all Virus, bacterial Plasmide or another system vector and their incorporation in an organization host inside of which they do not appear in a natural way, but where they can multiply continuously;

2) techniques implying direct incorporation in a hereditary organization of material prepared outside the organization, including the Microinjection, the Macro-injection and the Microencapsulation;

3) techniques of cellular Fusion (including the fusion of Protoplast S) or of Hybridization in which alive cell S presenting of new combinations of hereditary genetic material are consisted fusion of two cells or more by means of methods which are not implemented in a natural way.

On the other hand, this same directive specifies as:

is not GMO: organizations produced by Mutagenèse, or the cellular Fusion (including the fusion of Protoplast S) of vegetable cells of organizations which can exchange genetic material by traditional methods of selection.
is not regarded as involving a genetic modification (except use of Nucleic acid recombining or of GMO already obtained): the fecundation '' in vitro '', processes natural such as the conjugation, the transduction, the transformation, or the Polyploid induction .

Exchange genes in nature

The denomination of organization genetically modified refers to a artificial modification of the Genetic inheritance of an organization. But of the systems of natural transfer of DNA exist, and they lead to the appearance of organizations whose genetic material is transformed. The principal devices of natural exchanges of genes, of which some are exploited by the techniques of the genetic Engineering, are the following:

the Rétrovirus are Virus able to make integrate their genetic information in the Génome of their host. Thanks to sequences present on both sides of the viral DNA, which are recognized by the genome host, this last accepts its caesura and the integration of the viral DNA.

the Plasmide, which is a small circular molecule of DNA, is mobile and can pass from a cell to another. Some plasmides can then be integrated into the genome of the host cell. This form of transfer of DNA is observed for the Bactérie S, in particular for genes of resistance to the Antibiotique S. the integration of plasmide bacterial to the genome of a higher organization is limited to specific bacteria, and for given couples of species. Thus, Agrobacterium tumefacians is a bacterium of which a fragment of sound plasmide (the DNA T) is able to enter a vegetable cell and to be integrated into its genome.

the reproduction with individuals interféconds allows the exchange of DNA, between two individuals of two varieties, subspecies (intraspecific crossing), species (interspecific crossing) or kinds (intergeneric crossing) different. The Hybride thus produced presents a mixture of the genetic characteristics of the two parents.

the change S, by change of a Nucleotide by another, insertion or délétion of nucleotide sequences, can induce the appearance of diseases genetics S or of Cancer S. But the changes constitute also one of the engines of the evolution of the species.

Within the framework of the Endosymbiose, a whole of evolutionary processes led to the formation of Organite S (Mitochondrie and Chloroplaste) in the cells Eucaryote S, following the integration of bacteria and from Cyanobactérie S. the majority of the genome of the Endosymbiote was transferred in the core from the host.

Creative processes of the GMO and genes concerned

Techniques of genetic modification

Transformation of bacteria

; Transformation without integration in the chromosomal DNA

The Plasmide S of the Bactérie S are of interest to be easy to purify and to modify to integrate into it new Gène S. the transformed plasmide is built-in the bacteria where there remains distinct from the chromosomal DNA (except in the case of the épisome S), while being able to express gene of interest. The modified plasmide generally comprises a gene of resistance to a Antibiotique, which is employed as marker. Thus, only the bacteria having incorporated the plasmide are able to grow in a medium comprising an antibiotic, which makes it possible to select them.

Thanks to the important capacities of multiplication of the bacteria ( double Escherichia coli its population every 20 minutes), it is possible by this technique to have the genetic sequence of interest in great quantity.

On the other hand, the specificity of the systems plasmidic limits the bacteria able to incorporate the modified plasmide. Moreover, the instability of the transformation is worsened by the fact that the chromosomal DNA is not modified, and that the plasmide can itself be relatively unstable.

; Transformation with integration in the chromosomal DNA

The épisome S are additional Plasmide S having some Gène S coding the synthesis of enzymes of restriction which allow its integration the bacterial Chromosome S by a recombination épisomale.

Once integrated into the chromosome of the cell, the transmission of the genetic characters is ensured at the time of the Mitose of cells mothers in cells girls, contrary to the plasmides which are distributed in a random way.

Another means of proceeding to a transformation of bacteria with integration of DNA, is to use Transposon S. In certain bacteria, these let us transpose active can convey and make integrate gene of interest.

Transformation of plants and animals

; Indirect transfer of DNA or transfer by vector

Desoxyribonucleic acid (DNA), foreigner at the organization, is introduced into the organization of the host via a Virus, of a bacterial Plasmide or any other system biological vector. The vector and the host must be able to recognize themselves mutually, from where the specificity of the systems employed. By the genetic phenomenon of Recombination, the introduced DNA can be integrated in the Génome and involve the formation of a new combination of the genetic material. This new information must be able to be maintained in the genome on the following generations.

The principal techniques employed are the following ones:

Agrobacterium tumefaciens : this bacterium has a plasmide able to be integrated in the genome of the plants, which makes of it the vector most largely employed for the creation of plants transgenic. The Transgène is integrated in the plasmide this bacterium, which conveys it to the chromosomal DNA of the host. The gene of interest is not in all the cells, and it has a variable expression. For these two reasons, a phase of sorting is necessary.

Retrovirus: these viruses having the capacity to integrate their genetic material in the host cells to develop the infection, of the vectors were elaborate by replacing genes allowing the infection by a transgene. However, the retroviruses are very specific to their host, and these vectors cannot accept transgene of too large size.

Transposon S: this sequence of DNA transposable is used with a transgene to which were added at its ends of the sites of recognition of the DNA. The size of transgene must be limited. The techniques containing let us transpose are employed primarily on the Drosophile.

; Direct transfer of DNA

Organizations whose membranes are weakened or of the vegetable cells deprived of walls (such protoplasts) are put in contact with DNA. Then a physical or chemical treatment allows the introduction of the DNA into the cells. Other techniques such as the microinjection, the macro-injection and other techniques of Biolistique are based on the mechanical introduction of the DNA into the cells.

; Cellular fusion

The cellular fusion (including the fusion of protoplasts) or of hybridization in which alive cells presenting of new combinations of hereditary genetic material are consisted fusion of two cells or more by means of methods which are not implemented in a natural way.

Genes concerned

One can define six main categories of Gène S used.

Genes markers

It acts there, not of characteristic which one wishes to confer on the organization, but technical artifice allowing to identify and sort the cells into which desired genetic construction was introduced, of those where the operation failed.

The genes of resistance to antibiotics are used as simple and practical markers of selection: it is indeed enough to mend the cells in a medium containing antibiotic, to preserve only the cells at which the operation succeeded. The genes of resistance to antibiotics used (that one can always find in certain PGM currently) were those of resistance to the kanamycine/néomycine, ampicilline and streptomycine. Their choice was essential naturally, by the fact that they were of everyday usage to make sure of the purity of the microbe cultures, in medical research and biology, and, not even used little in human Médecine. Since 2005, they are prohibited for all new GMO.

Today, one employs more and more is a method of excision of these cassettes " genes of résistance" , not to more leave in place but the Gene of interest, so as to be sure that these genes of resistance do not interfere with the Phénotype observed, that is to say one carries out the transgénèse with a binary system (two plasmides: one carrying the cassette " gene of intérêt" , the other the cassette " gene marqueur". In the descent of plants GM obtained, only those which have the cassette " gene of intérêt" are retained.

Genes of resistances to the insects

This resistance is conferred on the Plante S by Gène S coding a truncated form of Endotoxine S proteinic, manufactured by certain stocks of Bacillus thuringiensis (bacteria living in the ground). There exist multiples Toxine S, active on various types of Insecte S: for example, certain plants resistant to the Lépidoptère S, such as the European corn borer ( Ostrinia nubilalis ), carry Gène S of the type Cry1 (A) .

Genes of tolerance to the weedkillers

They are for example genes conferring a tolerance on the glufosinate of ammonium (in Basta, Rely, Finale, Challenge, Liberty and Bilanafos) and on the Glyphosate (in the Roundup ).

Male gene of sterility

The male gene of sterility ( barnase ) code a Ribonuclease which is opposed to the expression molecules of Ribonucleic acid necessary to fruitfulness. It is controlled in order to be expressed only in the Grain of pollen.

The gene barstar , as for him, is an inhibiter of this ribonuclease, and returns its fertility to pollen.

The combination of two genes allows, for example, to prevent the Autofécondation in a pure variety carrying barnase , but to authorize the production of seeds by an hybrid of this variety and another, carrying barstar . Thus, one can obtain homogeneous hybrid seeds (used for salads in Europe), or prevent the re-employment of seeds.

Genes antisens or direction blocking the translation of other genes

The operation consists in introducing an additional specimen of a given gene, but in orientation (one reverses then speaks about gene “ antisens ”), or, sometimes, in the same direction, but truncated. The presence of this gene “ erroné ” decreases in a drastic way the stage of translation of normal gene, which prevents the synthesis of the enzyme coded by this gene. An example of this type is that of the Potato, whose synthétases are synthesized in limited quantities, in order to produce a different starch.

Genes used to carry out animals transgenic

Stakes

The GMO plants throughout the world

The regulation of the genetically modified organizations is very variable according to the countries; very diverse legal measures were taken in the world concerning research, the production, the marketing and the use of the GMO, in their various scopes of application (agricultural, medical,…). In Europe, these measurements are generally particularly restrictive.

Consequently, the surface cultivateds of GMO plants are very variable: anecdotic in Europe, strong growth in North America and in the emergent Countries.

Conflicts around the GMO

The GMO cause divergence great of opinion; the advantages brought by the GMO are opposed to potential health hazards and fears on a possible attack to the biodiversity.

Lobby anti-GMO

Lobby pro-GMO

Partisans of the GMO, whose European commission and the large seed-bearer ones like Monsanto, even if they rest on, according to them, an absence of proof of harmfulness of the GMO marketed, do not succeed in convincing.

In France, the Orema trade union, inter alia, which gathers producing corn, corn, the oléoprotéagineux one of FNSEA, invites not to yield not to the “merchants fear”.

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