Dont use the words in breeding. use the words breeding in. now it will make sense. Breed close relatives who both share the same feature together. If you breed two mice with the same fault together, you will give inbreeding or breeding in a bad name.(This fault can be lack of vigour, por fertility, etc ) The results are up to the breeders. It takes two generations to fix a true breeding colour. You can closely inbreed for thousands of generations if its done right.