When a plant or animal is bred with a plant or animal from different stock, the process is known as hybridization. There are numerous reasons to create hybrids, including increasing genetic diversity and breeding for specific traits. It is frequently practiced in agriculture, to make stronger, healthier plants with desirable characteristics. Animal breeders also use the process to create new breeds or to try to breed out unwanted traits, such as hip dysplasia in some purebred dogs.
The most common type of hybridization involves crossing two organisms of different breeds within the same species. This is also called crossbreeding. In agriculture, it is used to create healthier crops or new flavors, such as the tangelo, a cross between a tangerine and a pomelo. In agriculture, it is vitally important to maintain genetic diversity, and by extension the health and longevity of a crop. Many large agricultural companies engage in monocropping, planting only one strain of one crop, which is very harmful for diversity and for the plant. Should the crop be susceptible to a particular fungus or insect, the whole field will be lost. Hybridized crops, on the other hand, tend to be more resistant to disease and infestation.
In animal breeding, hybridization is used to create new breeds or to make a breed stronger. Many purebred animals are also inbred, due to a limited genetic pool, which tends to bring out genetic defects in animals. By hybridizing, breeders bring fresh genes into the mix, although the resulting animal is not a purebred. Depending on the rules of the stud book for the breed, this may or may not matter. In some cases, a crossbred animal can be bred to purebreds to bring the next generation more in alignment with the breed standard, and the mixed breed animals will be accepted into the studbook.
In another variation, two animals of different species within the same genus are bred to each other. This is not always possible, and when it can be achieved, the resulting animal or crop is often sterile. Most animals hybridized in this way, such as mules and zorses, a horse/zebra cross, cannot reproduce naturally. Plant hybrids, on the other hand, are usually perfectly capable of breeding. This will increase the overall genetic health of the plant population, and in some cases will bring out a desired trait, such as seedlessness.
Hybridization also occurs in nature, and it can bring out favorable traits from two different gene pools. It allows animals to adapt to changing environments, and if the hybrids thrive, a new species may emerge.