This means that you can't breed them in the traditional sense that we do with other plants. Outside of Granny Smith apples the ones you eat are mostly the results of mutations in the grown plants that we cut off and graft.
I think ancestral citruses (not the crosses) are the primary exception, as well as a few citrus hybrids which create clone seeds asexually.
> Outside of Granny Smith apples the ones you eat are mostly the results of mutations in the grown plants that we cut off and graft.
Honeycrisp is a chance seedling, though it stems from a horticultural crossbreeding effort it was grown from seed. And commercially useful sport mutations tend to come from popular chance seedlings to start with, since it is necessarily a more limited evolution of the basal cultivar, which needs to exist and in sufficient quantity that you’ll roll out useful mutations eventually (also useful is in the eye of the beholder as we can see with the red so-called delicious).
Plus they were not completely wasted, while not generally edible they’re fine for cider.
Not sure where you're located, but this isn't true in the US. The vast majority of apples available here are seedlings of crosses by two other varieties. Examples:
Golden Delicious, one parent is Grimes Golden, the other unknown.
Fuji, Red Delicious × Ralls Janet
Gala, Kidd's Orange Red × Golden Delicious
There are certainly some sports (the technical term for for the spontaneous mutations) like you mention. Royal Gala, available in NZ, is a sport of Gala. But most are not.
An enormous amount of industry effort goes into crossing known varieties, growing the seedlings, and looking for the apples with the best traits. Cosmic Crisp is a great example of a recent one.
Here's some more reading:
https://www.cumminsnursery.com/learn-trees/fruit-tree-bloom-...
https://www.cumminsnursery.com/learn-trees/fruit-tree-pollin...
Crab-apples are good for pollination IF they overlap flowering. Not so much otherwise. If you have an early flowering variety and a late flowering crab-apple forget it. You don't need them as a third apple may work perfectly.
In any case they are beautiful trees and excellent for wildlife. You will not be disappointed with the excellent spring and fall displays, but if the space is limited I would go for a different tree or a third real apple choosing carefully the rootstock. If you want a crab-apple put it at the background. (Optical effect. It makes the garden appear bigger). If you like to watch birds while sipping your coffee in the front.
Crab-apples would be the kings of garden if they didn't suffered from so many diseases.