Gene stacked event

A genetically modified organism (GMO) and all subsequent identical clones resulting from a transformation process are called collectively a transformation event. If more than one gene from another organism has been transferred, the created GMO has stacked genes (or stacked traits), and is called a gene stacked event.

Gene stacked events have become an important topic in plant breeding. Occasionally, researchers wish to transfer more than one trait (e.g. an insect resistance and a herbicide resistance) to a crop. Consequently, they need to transfer more than one gene, and do so either in one or in subsequent steps. This can be achieved either by genetic engineering or by conventional cross-breeding of GM plants with two different modifications.

In most contexts, the difference between a GMO with one new trait and a GMO with several of these is negligible. However, when the GM content of a harvest or any GM product is being measured, stacked genes may have severe consequences. Many countries require the labelling of GM products if the GM share of a single ingredient exceeds certain limits: for example, this limit lies at 0.9 percent in the European Union. Usually, this is analysed by measuring a genetic sequence common to most GMOs. This sequence is transferred along with the gene of interest, when a new GMO is created. A GMO with more than one transgene contains a corresponding number of copies of this sequence. Therefore, measuring the number of copies of this sequence in a food sample would return a figure twice (or more) as high as the actual GMO percentage. Researchers are trying to develop new measuring techniques to overcome this hurdle. Some of these projects are being conducted under the extensive European research programme on co-existence and traceability of GMOs, Co-Extra.