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What is gene flow and what are its possible consequences?

Gene flow is the movement of a gene from one plant population to another, and occurs naturally, keeping plant populations genetically connected. In contrast, the movement of transgenes from GM crops to populations of wild or crop relatives may be considered undesirable and there may be undesirable environmental consequences, such as more aggressive weeds, loss of germplasm, or increased non-target and biodiversity losses.

How can the risk associated with gene flow be assessed?

Step 1. Identify recipients of gene flow

By identifying the possible recipient plant populations (wild or crop relatives) and their geographic distributions in your country, it becomes possible to consider likelihood of gene flow and possible risks concretely.

• possible recipients of gene flow from Bt maize in Kenya

Step 2. Likelihood of gene flow and the spread of transgenes

The likelihood of transgene flow depends on the mating compatibility and the geographic proximity of the GM crop and the recipient population. Humans may also play an important role in gene flow by moving seeds from place to place. Spread of a transgene depends on the effect of the transgene on the fitness of the recipient population and the frequency of gene flow. By considering these simple factors, recipients at greatest risk can be identified.

• possibilities for gene flow from Bt cotton in Brazil
• possibilities for gene flow from Bt cotton in Vietnam

Step 3. Possible adverse effects

For the identified recipients, what is the possibility of an adverse effect? This can be:

• transgene contamination of seeds
• increased weediness with possible retention in the seedbank over several years
• loss of genetic diversity
• extirpation of the recipient population
• increased non-target or biodiversity risk
• increased resistance risk

These three steps allow a risk assessor to identify a smaller number of concerns that may require more detailed assessment. For such concerns, several experimental designs can be recommended to clarify the risks of gene flow prior to a commercial release.

'Moco' cotton in Brazil: a possible recipient of gene flow

cotton volunteer along a road in Brazil: bridging populations

species of Malvaceae

Gossypium barbadense bolls