How is a transgenic crop made?

The processes involved in making a transgenic crop are as follows:

• Identification of an organism containing the desired gene; this can be from a plant, animal, or microorganism.
• Isolation of the desired gene from that organism.
• Creation of a modified genetic sequence by the fusion of the desired gene, a promoter sequence, which controls the functioning of the gene, and a marker gene, for example, a fluorescent protein or an antibiotic resistance factor that allows the gene's presence to be detected even when the target gene is not being actively expressed.
• Multiplication of the recombinant sequence, usually in bacteria, to produce multiple copies.
• Insertion of the copies of the desired gene into the organism to be modified, using either a particle (gene) gun or a biological agent.
• Selection of those organisms that have successfully taken up the desired gene using a selection test that recognizes only organisms that have adopted the marker gene.
• Multiplication of the modified plants.

The modification made to a crop plant can relate to a factor of the plant that influences its physical characteristics. For example, one of the first GM foods was a tomato, the FlavrSavr tomato developed by Calgene. When natural tomatoes ripen, a gene is triggered to produce a chemical that makes the fruit go soft and eventually rot. With this gene modified, the FlavrSavr tomato has a longer shelf life and firmer fruit.