Geneticky modifikované organizmy

What are genetically modified organisms

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A genetically modified organism (GMO) is an organism whose genetic material has been altered using techniques in genetics 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. Thus, the abilities or the phenotype of the organism, or the proteins it produces, can be altered through the modification of its genes.

The term generally does not cover organisms whose genetic makeup has been altered by conventional cross breeding or by "mutagenesis" breeding, as these methods predate the discovery of the recombinant DNA techniques. Technically speaking, however, such techniques are, by definition, genetic modification.

Examples of GMOs are diverse, and include transgenic experimental animals such as mice, several fish species, transgenic plants, or various microscopic organisms altered for the purposes of genetic research or for the production of pharmaceuticals. The term "genetically modified organism" does not necessarily imply, but does include, transgenic substitution of genes from another species, and 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 used in researching the mechanisms of cancer and other diseases.

History of GMO

The first GMO was created in 1973 by Stanley N. Cohen and Herbert Boyer, demonstrating the creation of a functional organism that combined and replicated genetic information from different species. [1]. 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 concluded that recombinant DNA research should proceed but under strict guidelines. Such guidelines were subsequently promulgated by the National Institutes of Health in the United States and by comparable bodies in other countries. These guidelines form the basis upon which GMOs are regulated to this day.

The first transgenic animals were mice created by Rudolf Jaenisch in 1974. Jaenish successfully managed to insert foreign DNA into the early-stage mouse embryos; the resulting mice carried the modified gene in all their tissues. Subsequent experiments, injecting leukemia genes to early mouse embryos using a retrovirus vector, proved the genes integrated not only to the mice themselves, but also to their progeny.

Methods of genetic modification

Genetic modification involves genetic engineering, also known as gene splicing, a technique to splice together DNA fragments from more than one organism and thus preparing a "recombinant" DNA molecule in a test tube, producing a single piece of genetic material containing the original information from multiple fragments which can then be inserted into another organism. This is achieved by cutting up DNA molecules with restriction enzymes and splicing these fragments together using DNA ligase. A transgenic organism that contains such DNA sequences from a foreign organism integrated into its own genome, the term "transgenic" literally means across gene. A mouse or fish engineered to express the green fluorescence protein, for example, would be considered a transgenic organism, since the gene coding for the protein originated from a species of jellyfish.

With current technology, transgenic organisms can be produced with only a very small proportion of extraneous DNA. For example, the genome of most mammals contains three billion basepairs of DNA, while it becomes relatively difficult to insert more than 10,000 to 20,000 basepairs of foreign DNA. More sophisticated techniques using yeast artificial chromosomes and bacterial artificial chromosomes allow insertions of up to 320,000 basepairs [3] - approximately 0.01% of the total genome. In concept, multiple rounds of transgenesis or interbreeding of transgenics could lead to organisms with a higher proportion of foreign DNA, but cost and time considerations prevent this.

In order to introduce new DNA into the receiving host, vectors are used. Vectors range from small circular pieces of DNA such as plasmids, to various viruses that can carry and transmit genetic information. 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. The foreign DNA uptake is facilitated by the presence of certain cations, such as Ca2+, or by the use of electric current (electroporation). 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 protein called a pilus (a process analogous to but biologically distinct from mating). A plasmid is transferred through the pilus. Conjugation is not widely used for the artificial genetic modification of bacteria, but happens often in nature.

Transduction refers to the introduction of new DNA into a bacterial cell by a bacteriophage, a virus that infects bacteria.

In order to gain knowledge about a particular gene's function, researchers often use knock out organisms. These organisms have a specific gene that has been functionally 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 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.



© 2006 - Department of Biosafety - Ministry of Environment - Slovak Republic