Seed production represents a recombination of genes. For this reason, when you grow a specific variety of fruit the tree is a cutting from the original tree (e.g. meyer lemon) grafted onto rootstock. In other words, all meyer lemon trees are clones of each other.
Similar to fruit trees, vegetables (and other annuals) have been artificially selected into to different breeds/strains (e.g. beef steak tomato or beit alpha cucumber). How are the genetics preserved so that the seeds grow plants that are the same as the parents (“grow true”)? Even if they are grown in an environment free of other genetic contamination, just the fact that they are producing seeds means that there is some genetic recombination and the seeds won’t be identical to the parents.
The only thing I can think of is that seeds from plants of a specific strain (e.g. butternut squash) are not all identical (similar to how all golden retrievers are genetically similar but not identical, like meyer lemons are), however butternut squash don’t seem to have much variability. Meaning, when I grow them, they all look pretty similar to each other and similar to their parents.
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Note: I know that some plants are genetically engineered. I’m interested in how genetics were preserved before this was a thing.
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>Even if they are grown in an environment free of other genetic contamination, just the fact that they are producing seeds means that there is some genetic recombination and the seeds won’t be identical to the parents
This is very much easier for things that are insect pollinated, like squash, compared to things that are wind pollinated, like corn or wheat. For vegetables, it is easy, and you can maintain a dozen separate lineages in an acre. When the plant forms flower buds, you simply put a mesh bag over the bud to keep bees out. Then, you take pollen from one plant and carry it to another using a paintbrush. It may be necessary to use tweezers to destroy the pollen producing parts of a flower to prevent self- pollination. It is a fair amount of fiddly work, but each fertilized flower produces dozens or hundreds of seeds.
Wind pollinated plants have to be grown out in isolation. For example, GMO corn seed is mostly grown in Hawaii. Hawaii is very fertile, but the land is expensive, so people mostly grow high value crops like pineapple. No one is growing much corn, so they can plant it there. If you want to grow seed corn, even for your own use, and your neighbor wants to grow a different kind of corn, [you’re screwed.](https://www.reuters.com/article/us-monsanto-organic-lawsuit/organic-growers-lose-decision-in-suit-versus-monsanto-over-seeds-idUSBRE9590ZD20130610)
Most grocery store varieties of vegetables are hybrids. They maintain two different lines of tomato or squash or whetever, and cross them to produce seeds that farmers buy. If you plant the seeds from teh grocery store plant, it will never grow quite as big, because it isn’t a cross of those varieties. The hybrid has extra chromosomes- [polyploidy](https://www.mutagens.co.in/jgb/vol.04/3/18.pdf)
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