Worldwide mankind has domesticated more than 30 animal species for agricultural purposes (14 of these species are responsible for more than 90 % of the food produced by animals). In addition other animal species are domesticated for leisure purposes or for a variety of other services for mankind (hobby, guarding, nature management, hunting etc.). Within these animal species a lot of variation is observed. The animals of a species differ more or less in a lot of traits: they show diversity in nearly all traits. A diversity that has a genetic origin.
Within species we recognize landraces: within a landrace animals resemble each other but among individuals you still may observe diversity in a lot of phenotypic traits. Out of the landraces mankind created standardized breeds (and later on, out of these, special selection lines). In the standardized breeds animals resemble each other more than in landraces. They are more uniform; but still among individuals of standardized breeds diversity can be observed. To conclude: within animal populations (species or landraces or breeds or selection lines) diversity exists that has a genetic origin. The origin is determined by the fact that animals differ in their DNA composition: within a species more than in a landrace, within a landrace more than in a standardized breed and within a standardized breed more than in a selection line. A broad definition of genetic diversity is:
Definition
Genetic diversity is the set of differences between species, breeds within species, and individuals within breeds expressed as a consequence of differences in their DNA