Grafted apple trees are often a flavorful top connected to a weak root. Weak root = smaller trees that can be planted closer together and are easier to pick. If you plant apple seeds, you will probably get a ginormous tree with fruit only useful for cider making (a la Johnny Appleseed's business model) because they don't taste good either fresh or in baked goods.

I was lucky to get what I assume is a mutant avocado seed. I tried to grow six different seeds, germinated four, and only succeeded in actually planting one. Two didn't germinate, and the other three grew roots but the seedling was malformed and wouldn't grow out of the seed.

The one that survived must have had a mutation that allowed it to survive despite what was otherwise probably an intentional effort to produce sterile seeds.

Usually I hear "grafted," where you take one variety with strong roots, cut the top off of him, take another variety that makes the fruit you want, cut the roots off of him, and then put the good roots on the good fruit and tape them together. I've even seen one root stock grafted to several different species of fruit so the same tree grew apples, pears and pomegranates.

Apples don't breed true; a seeds out of a Gala apple won't grow a tree that makes Gala apples. They might be better, they might be worse, they won't be Galas. All commercial apple production is done by grafting branches of existing trees onto new root stocks.

I am just north of where peaches will properly grow. Doesn't stop people from trying. Every year in early spring there's a late cold snap, and every year people say "It's killin' my peaches." Every single individually wrapped year I hear that from someone.

I get you peaches, I also just barely survive the emotional coldness of a northern German winter.

counterargument, it's trivial to grow