Here is something I find very interesting.
As you know, some Pembroke Corgis are born tail-less (bob tailed), And it is an important reason why Pems have their tails docked - to conform. But one should never mate a naturally tail-less Corgi with another naturally tail-less (or bob tailed) Corgi. The reason is the risk of serious genetic problems that might arise with the off-spring. So there is never going to be a natural race of tail-less Pem Corgis. There are one or two other breeds of dogs and I believe a breed of cat where the same scenario applies.