Genetic Modification

Genetic Modification of plants

The principle technique for the genetic modification of plants is based on a natural ability of the bacteria Agrobacterium tumefaciens. This bacteria infects plants and causes a tumor-like growth termed a crown gall. Agrobacterium causing crown galls 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. By 1983, biotechnology had reached the point where it was possible to insert additional genes of interest into Agrobacterium and thus transfer those genes into plants.

Genetic Modification of animals

Animals can also 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.

Genetic Modification of bacteria

Three processes are known by which the genetic composition of bacteria can be altered: transformation, conjugation and transduction.
- 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 Fred 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.

- In conjugation, DNA is transferred from one bacteria to another via a temporary connecting strand of DNA 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).


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