You can get rid of any fault by in breeding even if both of your origional stock have the fault, but you do have to cull without question,to purefy the genes. I always try to remember that genes from both parents divide and rejoin randomly to form whole genes again in the offspring. This is simplifying it but its easier to understand. If you think of a gene as being a whole thing but made up of two parts.It can be DD double dominant, DR Dominant/recessive or RR double recessive. Thats how you can breed together two dogs that both express eg, determination but neither are pure DD for that trai