Purebred

Purebreds are cultivars of an animal species achieved through the process of selective breeding. When the lineage of a purebred animal is recorded, that animal is said to be pedigreed. Purebreds breed true-to-type, which means the progeny of like-to-like purebred parents will carry the same phenotype, or observable characteristics of the parents. A group of like purebreds is called a pure-breeding line or strain.

True breeding

In the world of selective animal breeding, to "breed true" means that specimens of an animal breed will breed true-to-type when mated like-to-like; that is, that the progeny of any two individuals of the same breed will show fairly consistent, replicable and predictable characteristics, or traits with sufficiently high heritability. A puppy from two purebred dogs of the same breed, for example, will exhibit the traits of its parents, and not the traits of all breeds in the subject breed's ancestry.

Breeding from too small a gene pool, especially direct inbreeding, can lead to the passing on of undesirable characteristics or even a collapse of a breed population due to inbreeding depression. Therefore, there is a question, and often heated controversy, as to when or if a breed may need to allow "outside" stock in for the purpose of improving the overall health and vigor of the breed.

Because pure-breeding creates a limited gene pool, purebred animal breeds are also susceptible to a wide range of congenital health problems. This problem is especially prevalent in competitive dog breeding and dog show circles due to the singular emphasis on aesthetics rather than health or function.