Or differing in every single gene they didn’t happen to measure, which is a lot of them
It took nine genes to take wild tiosinte and turn it into modern maize
It was probably a self pollinated seedling, which, while similar to the parent often express differences
Just because the tree suckers doesn’t mean that it is a seedling. If you are implying that it is a seedling because the suckers match the parent, that just means that the rootstock matches the top, which could also occur from a rooted cutting, or someone planting a sucker from the original Sherwood.
I’m actually not sure if I’ve gotten any fruit from the grafts yet. But it doesn’t surprise me if your fruit is similar, but there is a difference in productivity. Many of my trees have differences in productivity, even as identical cultivars. They could also be a branch sport, a mutation, which increases the productivity. It’ll be interesting to see if other people experienced the same benefit.
I think this test looked at 147 different genes (SNPs). The chance for a self pollinated seedling (I’m not sure if that is even possible for Sherwood) to match on a given single gene is 50% if the gene is xy and 100% if it is xx or yy. Even if you figure that only 20% of those 147 were xy, the chances of them matching for a seedling is just 1 in 536 million, 2 to the 29th power. There may be other options at work that I don’t know of, but based on the study, I don’t think it would be a straightforward self pollinated seedling.