The seeds from a grafted tree is no different to the seed from a tree growing on its own roots. Grafting is a way of propagating trees asexually, so that genetically, above the join with the rootstock, the trees are identical. All Bramley apple trees are clones of one original Bramley which was selected from a sexually diverse group of trees for the qualities of its apples.
One other benefit of grafting is that you can choose to use rootstock that won't allow the tree to grow very big, or that has resistance to some soil borne disease.
