There is a part of truth on all opposites considerations.
The sex is hardcoded yes but not in the way “male/female/herm”. They can be only one of them, both of them or all of them with different biological priorities.
“Pure” specimens being really rares in practice even in the most stabilized lines (which no longer exist today on the market outside the underground).
Its expression (of sex) is not hardcoded also, and it’s why “feminized” seeds exist. You need a latent “female herm” with a specific artificial expression (spray) to create a “good/bankable” fem line (sic). In this post i enter more in details about it.
I will dare to make a simple synthesis to separate the twos concepts :
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seeds : the whole possibilities of expression of each specimen is determined for good. Which don’t mean than it’s the reflect of the genetic potential for further generations at all. If you hybridize a rockstable latent female-herm than never trigger herm in normal condition, you can expect worries in its offspring and years of “washing/stabilization” behind.
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plants : the word “epigenetic” is trendy and often used for all and nothing, but in this specific case i can’t find a better word to be accurate. With the environment, you will reveal the true priorities of the specimen. Let’s take the case of “feminized seeds” again (they are absolutly not “feminized” in practice, but more “male’s depressed (not suppressed) for one generation”). It’s why than even the most greedy breeders assume in their marketing than fems seeds are not genetic materials but “seed to smoke” only : potential.
The epigenetic trigger to turn you best latents in pollen producer, is simply the STS in this case. Like the cold/blue etc … It don’t change at all the genetic (it’s too fast) but temporary its expression at the “H” hour. It’s mainly why today you can find so much “double-fem” garbage, it’s a manner to extend the rentability of one line on which you have no control or program. By choice generally, maintaining a genpool is expensive and take years. With this way, you can stay “trendy” in micro-cycles of 6 months until the next “sandwich of the month” … and for very cheap in comparison.
In another hand, to quote the other extreme, if this selection is made naturally by a stable environnemental factors during decades… you will change the code. If the “green” phenos are hungry in N but the soil is only rich in K, naturally they will extinct with their “sub-groups” in favor of specimens than are more compatibles with the soil.
So take care when you consider this aspect, the time involved in the operation is responsible of the type of the output. Generally the grade also but it’s another story.
Also, it’s important to split the potential of a seed (virtually for the eternity, like the human code) and the expression of this potential in a plant at one moment.
For different sources and inspiration, you can find a bunch of grouped readings here.