Some breeds of dogs that have been obtained by selective breeding.

By selecting parents carrying the alleles that influence traits desirable to humans, dog breeders have produced breeds with distinctive features. For example, the French bulldog has alleles that give it short legs and a flat face. All the dogs shown in this figure carry the same kinds of genes (for example, genes that affect their size, shape, and fur colour). However, the alleles for many of these genes are different among these dogs, thereby allowing humans to select for or against them and produce breeds with strikingly different phenotypes.