<P> Purebred breeding aims to establish and maintain stable traits, that animals will pass to the next generation . By "breeding the best to the best," employing a certain degree of inbreeding, considerable culling, and selection for "superior" qualities, one could develop a bloodline superior in certain respects to the original base stock . Such animals can be recorded with a breed registry, the organization that maintains pedigrees and / or stud books . However, single - trait breeding, breeding for only one trait over all others, can be problematic . In one case mentioned by animal behaviorist Temple Grandin, roosters bred for fast growth or heavy muscles did not know how to perform typical rooster courtship dances, which alienated the roosters from hens and led the roosters to kill the hens after mating with them . </P> <P> The observable phenomenon of hybrid vigor stands in contrast to the notion of breed purity . However, on the other hand, indiscriminate breeding of crossbred or hybrid animals may also result in degradation of quality . Studies in evolutionary physiology, behavioral genetics, and other areas of organismal biology have also made use of deliberate selective breeding, though longer generation times and greater difficulty in breeding can make such projects challenging in vertebrates . </P> <P> Plant breeding has been used for thousands of years, and began with the domestication of wild plants into uniform and predictable agricultural cultigens . High - yielding varieties have been particularly important in agriculture . </P> <P> Selective plant breeding is also used in research to produce transgenic animals that breed "true" (i.e., are homozygous) for artificially inserted or deleted genes . </P>

How can animal or plant breeders use mendelian principles