How many Saiyan/Human breeds would it take to become 100% Human

So I've been wondering about this for a very long while. If Goku Jr. (An Eighth Saiyan) is still able to go Super Saiyan, then how many times would that bloodline have to divide in half to make a Saiyan breed no longer Saiyan and in turn removing Saiyans and Super Saiyans all together? It seems just having Saiyan blood is enough to eventually turn Super Saiyan after the proper training? If both Goku Jr. and Vegeta Jr. could go Super Saiyan, then what stops their kids, grandkids, great grandkids, and so on so forth from becoming Super Saiyans? If a child from Vegeta's descendents and a child from Goku's descendents make a child, does that restore some of the Saiyan bloodline or would we have a centaur theory where it could be 1 of 3 things? All Human, all Saiyan, or still both human and Saiyan?