One such risk scenario is the possibility that the genes coding for the novel traits may be transferred into the environment. This is known as introgression and can occur via horizontal gene expression or through cross breeding between the LMO and sexually compatible species that are present in the likely potential receiving environment.

Gene flow followed by undesired introgression of the transgene in species of interest – Gene flow is a term used to indicate the transfer of genetic material from one population or species to another. Gene flow may be horizontal (i.e. without involvement of sexual crossing) or vertical (e.g. seed production via pollen).

In the case of plants, vertical gene flow may occur even between organisms that are located far apart since pollen can be carried across large distances by the wind or insects, for instance.

The potential for gene flow from an LMO to non-modified organisms is first evaluated by investigating if sexually compatible species are present in the likely potential receiving environment. If sexually compatible species are present, there is a possibility of gene flow from the LMO to these species. Whether or not the modified genetic elements can potentially introgress into the population of the sexually compatible species will be largely determined by the biology of the recipient organism and of the LMO itself (see considerations regarding the likelihood and consequences of gene flow and introgression in sections 5.2 and 5.3).