The transgene design controls the trait
Agronomists and others who work with crop plants have become accustomed to the terms ‘Bt’, ‘event’, and ‘Cry’ protein when describing the newly introduced resistance to some insect pests. Figure 3 summarizes graphically the structure of transgenes that encode Cry proteins for ECB control. The following key facts go along with this figure and are considered a part of a professional agronomist's working knowledge on how transgenic technology is used to introduce new traits.
1) A transgene is a sequence of DNA assembled and copied outside of the plant and then introduced as an additional gene into the chromosome in a living plant cell. The gene introduction is called an event.
2) The transgene is copied as the chromosome is copied from cell to cell and eventually to the next generations of plants through normal seed production.
3) Transgenes work according to the normal principles of the other genes in the chromosome. They must have promoter sequences which tell the cell how they will be turned on and off and they must have coding regions to specify the protein encoded by the gene.
4) The protein actually controls the metabolic activities in the cell. In the case of ECB resistance, the transgene encodes a protein (Cry protein) that is an endotoxin specific to ECB larvae.
5) The genetic engineer can design and assemble a transgene with a desired promoter and coding region. How they assemble this transgene will dictate how the trait is expressed in the plant.