In traditional breeding, cross-breeding of different varieties within the same species is used to modify successive generations, so the greater the gene pool and the more distinctive the characteristics of a variety are, then the easier it is to breed special varieties as one wishes.
以傳統育種來說，因為是經由同一物種不同類間的配種交配來改良子代，因此品種基因庫愈大、愈有特色，就愈能隨心所欲培育出自己想要的特殊品種。