oh that is good news - I had this idea in my mind - I'd been told not to use seed from grafted trees way back when. Really all that information I absorbed about gardening as a young thing has proved excellent but maybe not this one - the idea was that you didn't know what you were getting in the seed, was it from the rootstock or the graft. I have had the first fruit off my mango tree grown from the seed of my big mango tree which being a Kensington Pride is likely to be grafted and it was very good too.
I was watering my avocado seedlings today and the Siamese twin is a double double - each side has now split into two, there are 4 crowns developing and fascinatingly the stem is reshaping into a solid round shape instead of the fluted look lower down.