All living organisms are made of cells which contain DNA. The Units of DNA molecules are called genes. The genes contain the information that is used by the cells as recipe for the organism.
It has been discovered that DNA is interchangeable among animals, plants, bacteria and other organisms.
In addition to using the traditional breeding methods, for improving the plant or animal species through cross breeding and selection, scientists in some cases now can transfer the genes that determine many desirable traits from one plant or animal to other.
The transfer of DNA is done by various methods such as direct injection of cells with DNA or literally shooting cells with DNA Covered Particles from a special gun called gene gun.
Another widely used method is to insert the DNA into specifically modified bacteria or viruses, that carry it into the cells they infect.
Regardless of which method is used, the general purpose of the process of transferring DNA from one organism to another is called genetic engineering. Technically, almost any desirable trait found in nature can be transferred to any chosen organism. A plant or animal that is modified by genetic engineering to contain DNA from an external source is called transgenic organism. The uses are unlimited such as Pharma, gene therapy and the development of transgenic plants and animals such as Glofish which is the first commercially sold transgenic animal to be sold as a pet. These organisms are called GEM or genetically modified organisms.