Pears grown from seed saved from the fruit of a grafted tree...or volunteers from deer eating/dropping from the same, will produce very small, inedible pears for deer or man. (about the size of a ping-pong ball or smaller) I've tried it. The tree will reproduce their wild stock state. I've not tried apple seed planting but I think the same thing will occur.
I'd buy and plant quality grafted saplings for optimal results.