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Comment by h0l0cube | Hacker News Reader

Thank you, and excuse my naivete here. So what makes the hybrid route the optimal way to produce these GM plants, rather than cross-breeding in a way that survives reproduction? Do we know GM crops to always be hybrids of this nature?

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The way I understand it (I took a course in this 5 years or so ago but might not remember correctly) it's a matter of ease of matching up certain chromosomes. Like people, plants tend to have chromosomes in multiples (though not necessarily 2). From one generation to the next, for a given set of chromosomes, a parent only passes half on to the child, and this is pretty much random. That means that for a plant breeder it's very undesirable to have parents with genetic diversity: this diversity results in randomness (unpredictability) in the offspring. BUT you don't want offspring that has identical copies for all these chromosomes because those are not strong genotypes (this is where the hybrid vigor comes in, you want plants with diverse chromosomes). The solution that plant breeders have found is that you take parents which have copied chromosomes, but you take 2 different parents and you control who the parents are. That way the offspring gets a mix, but the content of that mix is highly predictable.

Some side issues are that the parents are only suitable for breeding (they don't have strong genotypes themselves) and that if you take this offspring and mix them again you get a genetic shuffle which reintroduces unpredictability. This second generation will also perform very poorly, or at least unpredictably.

For seed companies you can tell that this is attractive in 2 ways: they can produce quality seed relatively easily, and the farmer always needs to buy the seed that they use for production because the farmer does not have the parent plants and the second generation is unusable.

A mule is a hybrid. It's bigger and stronger than either a donkey or a horse. It is infertile. It's the same with your garden variety hybrid corn or tomatoes. Big easily stotable and shippable product (but without flavour or desirable texture), but is infertile or doesn't breed true.

Not all hybrids are infertile. Maize corn was developed from its wild progenitors through centuries of genetic modification through selective hybridization -- it is not a plant found in nature -- and that required viable offspring. The same goes for other major crops developed by scientists in the past few centuries, like potatoes, tomatoes, and peppers (interesting pattern there, they all originated in the same part of the world).

It's incorrect to conflate hybridization with modern direct gene manipulation (GMO). They both have the same goal, and effectively do the same thing, but are completely different approaches. Hybridization requires the cross-breeding of unrelated varieties or species, and involves both genetic and epigenetic selection. GMO is directly splicing genes of a single organism to produce altered offspring. Don;t confuse the two.

Hybrid vigor https://en.wikipedia.org/wiki/Heterosis

It lets you create a sort of super crop... but it only works for a single generation. ‾\_(ツ)_/‾

It's not just GM plants. In fact, the GM crops might not even be hybrids at all (I don't really know). But many fruits that we love, like most citrus fruits, as well as bananas, are the result of cross-breeding between different species.

Why is this optimal? Well, I guess it isn't always. I'm willing to bet there are more failed hybrids than successful ones, but sometimes when you combine traits from different species, you get something that's bigger or tastier than the originals.

I have no idea about other crops; I was under the impression that grain and many other common crops could be replanted, but maybe it can't.

Also, as someone said above, this predates GM, its unrelated.

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