A responsible breeder will first assure that all the environmental circumstances are given for his cats to live in a healthy, stress free environment, with the substantial care he can provide them. He will have good knowledge of his breeds and their genetic beckground and adjust his breeding system to maintain the general and genetic health of each individual, his line and the breed in general and therefor share his experiences with other breeders.The average breeder, who wishes to establish a unique line is usually extremely careful in the selection of his individuals and uses a moderate amount of inbreeding to develop and fix beneficial characters. A breeder who desire extreme expression must be more patient as the genetic proportion of variation is usually very small He will chose Out-Crossing and grading-up methods in the hope that individual cats will show the desired characters.The breeder tries to regulate the breeding outcome, but as genetics can be unpredictable he might face unexpected circumstances. If unbeneficial effects occur the breeder must always exclude the cats from breeding and if they occur repeatedly face the possibility that negative genes might have been fixed in his line and face the consequences. Only if breeders work together to keep the breeds healthy, they have good chances to progress in some features. Taking Persian cats again as an example, they were for a long time bred for an extremely flat face and short nose, leading to sinus ailments, running eyes and breathing problems. Today breeders try not to produce this very extreme expression anymore. Persians are not allowed to have the nose higher than the bottom of the eye. New breeds have been extablished, the Bengal and the Savannah for their wild appearance, the Rex and LaPerm cats for their curly hair. Some trends, for example the aim of producing white cats and Munchkin cats must critically be evaluated.