Zacamo: I said grafting, not splicing. That is the technique that Digitally Analog crudely explained. He questioned whether there was genetic mixing between grafted plants. I answered that there isn't; but there is phytochemical mixing.
Splicing is an old term usually refering to genetic mixing. As despise said; selective breeding involves BREEDING plants/animals with traits you want together, which is a little tricky with chronic, as it is dioecious (can be male/female/hermie).