I recently watched a youtube video about why avocados cannot be grown by seed and learned about grafting. Interesting stuff. Didn't know apples also were grown through grafting.
There's an interesting discussion in Gun, Germs, and Steel where Jared Diamond claims that wild apples were inedible (IIRC due to cyanide in the seeds) and could only be domesticated after the invention of grafting technology.
also give a read about those green apples. (Granny Smith?). IIRC, all of these are grafts from one single tree. cmiw pls .