Transgenic Organism, plant, animal, or bacteria that has been genetically modified to contain a gene from a different species. The new gene is inherited by offspring in the same way as the organism’s own genes. The transgenic condition is achieved by injecting the foreign gene into the fertilized egg or into embryonic cells. The injected gene becomes part of the host cell’s deoxyribonucleic acid (DNA) within the chromosome and is then inherited by all the cells produced during embryonic development. It is thus present in all the cells of the resulting adult organism and is inherited by all its descendants.
This technique can be used to generate animals or plants that express genes conferring, for example, improved meat yield or resistance to specific diseases. It can also be used to create organisms that function as biological factories manufacturing hormones and other biological compounds used to treat human diseases. For example, bacteria can produce the hormone insulin, which is used to treat diabetes. Such uses of transgenic organisms are widely referred to as genetic engineering.
Transgenic organisms have proved very useful in analyzing the function of gene products because a specific gene can be expressed in all the cells of a transgenic organism and the effect on the organism’s development and function can then be monitored. It is also possible to use transgenic procedures to produce animals in which a specific gene has been deactivated in all its body cells. Certain genetic disorders of humans can be studied with this technique in laboratory animals if the disease-associated gene occurs naturally in both humans and an appropriate study species, such as a mouse. In such human disorders, symptoms are caused by natural dysfunction of the gene. In the study animal the same gene can be deactivated or made dysfunctional, causing symptoms similar to those of the human disorder. Scrapie, a fatal disease of the brain in sheep and related to human Creutzfeldt-Jakob disease, has been studied this way.