The term 'event' is often used to differentiate genetically engineered crop varieties. An event is the insertion of a particular transgene into a specific location on a chromosome. Once an event is produced in a single cell, it is perpetuated from cell to cell when the chromosome replicates and the cells divide regenerating a complete plant.
The event is then passed from parent to offspring through the gamete cells, which carry a copy of the parent’s genetic information. Eventually, these events end up in farmers fields as they are passed on through plant breeding and seed production. The three factors that differentiate events are:
- Which transgene was inserted (see modifying transgenes)
- Where on a specific chromosome it inserted (the locus)
- How many transgene copies inserted at that locus
The images below depict a transformed cell when the transgene enters the nucleus and inserts into the chromosome. The position of insertion of the transgene DNA into the chromosome is not predictable and varies between each event. The number of insertions per cell using Agrobacterium is assumed to be between 1 and 2 while several insertions may occur from particle bombardment. Moreover, Agrobacterium transforms a higher percentage of cells than particle bombardment. Therefore Agrobacterium is the preferred method of gene delivery to establish events.