Outcrossing

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Outcrossing is the practice of introducing unrelated genetic material into a breeding line. It increases genetic diversity, thus reducing the probability of all individuals being subject to disease or reducing genetic abnormalities(only within the first generation). It acutally can serve to increase the number of individuals who carry a disease recessively.^{[citation needed]}

It is used in line breeding to restore vigor or size and fertility to a breeding line.

Outcrossing is now the norm of most purposeful breeding, contrary to what is commonly believed.^{[citation needed]} The outcrossing breeder intends to remove the traits by using "new blood". With dominant traits, one can still see the expression of the traits and can remove those traits whether one outcrosses, line breeds or inbreds. With recessives, outcrossing allows for the recessive traits to migrate across a population. It mau actually increase the number of individuals carrying a disease. The outcrossing breeder then may have individuals that have many deleterious genes that are expressed by placing their animals against a similarly outcrossed individual. There is now a gamut of deleterious genes within each individual in many breeds.^{[citation needed]} However one may increase the variance of genes within the gene pool by outcrossing, protecting against extinction by a single stressor from the environment.

Outcrossing is believed to be the "norm" in the wild.^{[citation needed]} However, it is not logical as migration occurs by necessity. Feral cats, for example are one of the most inbred as individuals remain nearby their original homes, unless environmental stresses drive them to migration.^{[citation needed]}

Breeders inbreed within their genetic pool, attempting to maintenain desirable traits and to cull those traits that are undesirable. When undesirable traits begin to appear, breedings are selected to determine if a trait is recessive or dominant.^{[citation needed]} Removal is accomplished by breeding two individuals of known genetic status, usually they are related.

In nature, where breeding is not managed, outcrossing rates may be estimated by genetic analysis. This allows calculation of the amount of genetic exchange between populations, and thus provides insights into the biogeography and phytogeography of species.

Gregor Mendel used outcrossing in his experiments with flowers; as opposed to selfing.