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Consider the above multiple choice question. I can't seem to understand why the answer is B. How does genetically modifying the crop plant have any effect on the weeds?

The way I understand genetic engineering is that we insert a desired gene into the crop plant that allows it to become herbicide resistant. So how would this gene make its way to the weed? Could someone please explain how the two effect one another?

  • $\begingroup$ Why would you want herbicide resistance in the crop? How would you grow the crop to make use of the herbicide resistance? What is the treatment that you're presumably applying to both the crop and the weed? What are long-term results of that treatment? Try searching the internet a little bit; we usually ask that of people posting questions here, to show some evidence of research effort. $\endgroup$ Oct 21, 2022 at 21:48
  • $\begingroup$ "So how would this gene make its way to the weed?" That doesn't really matter for your question. (Evolution - selective pressure - is the answer to that concern. It is exactly like antibiotic resistance.) Just looking at the information presented, look at the advantages. What are they? What would interfere with the advantages? That's your answer. $\endgroup$ Oct 22, 2022 at 2:32
  • $\begingroup$ @MaximilianPress Herbicide resistance is desired so farmers can wipe out weeds without damaging crops. So we apply the herbicide to both the weed and crop so over the time the weed may mutate to become resistant? Could this be right? $\endgroup$
    – user73245
    Oct 22, 2022 at 3:50
  • $\begingroup$ @user73245 can you find any supporting evidence for that chain of logic on the internet, wikipedia, scholarly articles, etc.? $\endgroup$ Oct 22, 2022 at 4:36

1 Answer 1


I am pretty sure that the gene is not transferring directly from the crop into the weed. Instead, the idea is that you would never engineer an herbicide-resistant plant unless you were planning to apply herbicides to it. Since weeds will experience the effects of the herbicides along the GM plant (this is what kills them, after all), they will experience a selective pressure that may cause them to become herbicide-resistant.

  • $\begingroup$ What makes you sure that horizontal gene transfer doesn't occur in this case? Could you add a reference - else risk downvotes/deletion. (I'd assume the same thing as you because of the timing of the application - if before flowering and seed development, but we like references.) $\endgroup$ Oct 28, 2022 at 6:01

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