I got into a small argument :-)

Friends of mine try to draw fat line between "natural" selective breeding and applying molecular biology (CRISPR/Cas9) to put new traits in existing species. The line of their argument is "GMO is something different, because you can't (in reasonable timeframe, ~1000 years) breed a sheep that will glow in the dark.

Intuitively I think that doing so is possible even without molecular tools to "write" new genes, just using things like horizontal gene transfer and "standard" breeding (I reserve right to use all modern knowledge and tools to plan and monitor progress). I don't have much to substantiate this claim though.

In your enlightened opinion, who is correct?

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    $\begingroup$ We welcome new posters to SE Biology but ask them to read what sort of questions we encourage here, namely "questions about an actual problem you have faced", and those we don't, namely, questions the answers to which will be subjective. We are not here to arbitrate hypothetical arguments, even if we do have our own opinions, "enlightened" or otherwise. $\endgroup$ – David Apr 18 '19 at 16:54
  • $\begingroup$ Understood, and sorry if I did not adhere to guidelines - I can only say that is a community I trust to give me valid answers, hence I asked here. $\endgroup$ – StanTastic Apr 19 '19 at 8:18
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    $\begingroup$ Welcome to Bio.SE. Very interesting idea and I am definitely bringing this up at lunch! I think framing your question as a debate between GMO and selective breeding isn't clear. A more format friendly way of getting your answer would be "Has bioluminescence ever been selectively bred into animals or plants?" Remember to show evidence that you've attempted to answer the question yourself (maybe check google scholar). Also, note that CRISPR is not the only way to introduce specific genetic changes into organisms. $\endgroup$ – James Apr 23 '19 at 10:09

Natural horizontal gene transfer in higher animals is possible, but still very rare.
If any transfer happens then it's usually from micro-organsims (viruses/bacteria) or parasites to the host animal (or the reverse). Transfer of genes from any other source to animals is almost unheard of, because the transfer needs to affect the germline (sperm / eggs) to last more than a single generation and anything that doesn't live inside an animal is unlikely to get there.

Therefore your example of getting GFP (or any other fluorescent gene) into a sheep is highly unlikely$^1$, even with a 1000 year timespan.
You'd need a virus or bacteria that has a fluorescent gene and naturally infects/lives in/on sheep. However, no natural bacteria or viruses have a fluorescent gene in the first place (they almost all come from corals or jellyfish). Another problem is that just having a fluorescent gene somewhere in the DNA, doesn't mean the any part of the organism is fluorescent; once its in the gene pool this should be achievable by breeding though.

  • You'd have to wait for HGT of a fluorescent gene from a source animal/life form to bacteria. (Time estimate is super hard, you can maybe house some of these jellyfish in a fish tank regularly sequence the bacteria that live with them to see if HGT happened.)
  • Then the genes needs to be transfered to a bacterial/virus strain native to sheep (This is relatively easy/fast, since bacteria are quite proficient at HGT between each other)
  • Lastly you need a 3rd round of HGT from the bacteria to the germline of the sheep. (Again this might take 'forever': most mammals don't like bacteria or viruses living in or near their reproductive organs. Also at least from this point on animal experiment laws will become a serious hurdle to your project).

1) This is a researchers highly unlikely: without trying this, its not correct to say impossible, but the chances are so low that for all practical purposes it might as well be impossible.

  • $\begingroup$ Great answer, thank you :-) I actually thought about using fluorescent bacteria to start with, but this only cuts time in half, not in orders of magnitude :D $\endgroup$ – StanTastic Apr 19 '19 at 8:20
  • $\begingroup$ Perhaps you can add that even if someone infects the animal with a bacteria/virus carrying a foreign gene, that is still artificial genetic modification (albeit an inefficient technique compared to CRISPR-Cas). $\endgroup$ – WYSIWYG Apr 25 '19 at 8:22

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