I've done a little research on nucellar reproduction in citrus, and I understand that it's associated with several different groups of genes. It seems that there's no single collection of genes responsible.
I've also encountered some lists of types of citrus that have monoembryonic seeds, including specific cultivars or varieties of some species that vary on this trait. And some of them (I'd have to go back and doublecheck, but I distinctly recall noticing several) are the result of crossing two or more citrus types that are characteristically polyembryonic and nucellar.
I can easily understand that crossing a true-breeding nucellar plant with a sexually-breeding one might or might not result in a plant that clones itself. Given the right combinations of genes, I can even understand how two sexually-breeding plants could result in an apomictic one.
*edited to change treat to trait
But how in the world can a forced cross between two highly nucellar types of citrus result in a plant that breeds normally?
I'm particularly interested because I want to try making new citrus varieties from dwarfed, potted plants at home, and the most cold-hardy citruses I can locate are all true-breeding nucellar types.