外交配、他家生殖

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/10/03 14:19:51」(JST)

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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.

It is used in line-breeding to restore vigor or size and fertility to a breeding line. "Linebreeding", is where animals carry a common ancestor in their pedigrees and are bred together, should be considered distinct from the term "in-breeding" which is the production of offspring by parents more closely related than the average.^[1]

Outcrossing is now the norm of most purposeful breeding, contrary to what is commonly believed.^[2]^[3]^[4]^[5] 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. 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.^[6] However one may increase the variance of genes within the gene pool by outcrossing, protecting against extinction by a single stressor from the environment. In cats, there is currently a study running to determine the genetic diversity within the cat breeds.^[7]

Outcrossing is believed to be the "norm" in the wild.^[6] 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 maintain desirable traits and to cull those traits that are undesirable. When undesirable traits begin to appear, mates are selected to determine if a trait is recessive or dominant. Removal is accomplished by breeding two individuals of known genetic status, usually they are related.^[8]

In nature, where breeding is not managed, outcrossing rates may be estimated by genetic analysis, by employing mathematical models of mating systems such as the mixed mating model or the effective selfing model. 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 for his breeding stock. He then used the resulting offspring to chart inheritance patterns, using the crossing of siblings, and backcrossing to parents to determine how inheritance functioned.^[9]

References[edit]

^ Guy Fawkes Horses Retrieved on 2009-8-1
^ Cat Fanciers: American Curl: Cat Breed FAQ
^ The Balinese Cat in the UK
^ Inbreeding: A Personal Point of View
^ Outcrossing in hunting dogs
^ ^a ^b Price
^ http://faculty.vetmed.ucdavis.edu/Faculty/lalyons/Sites/FIS.htm
^ [1]
^ Mendel's Paper (English - Annotated)

English Journal

Strigolactone pathway genes and plant architecture: association analysis and QTL detection for horticultural traits in chrysanthemum.

Klie M1,2, Menz I1, Linde M3, Debener T1.
Molecular genetics and genomics : MGG.Mol Genet Genomics.2016 Apr;291(2):957-69. doi: 10.1007/s00438-015-1155-y. Epub 2016 Jan 19.
Chrysanthemums are important ornamental plants with abundant phenotypic diversity. Especially in cut-flower breeding, shoot branching is important for the success of new varieties. To assess the genetic regulation of shoot branching and other horticultural important traits, we phenotyped and genotyp
PMID 26780913

Recent mating-system evolution in Eichhornia is accompanied by cis-regulatory divergence.

Arunkumar R1, Maddison TI1, Barrett SC1, Wright SI1.
The New phytologist.New Phytol.2016 Mar 15. doi: 10.1111/nph.13918. [Epub ahead of print]
The evolution of predominant self-fertilization from cross-fertilization in plants is accompanied by diverse changes to morphology, ecology and genetics, some of which likely result from regulatory changes in gene expression. We examined changes in gene expression during early stages in the transiti
PMID 26990568

Reproductive patterns, genetic diversity and inbreeding depression in two closely related Jumellea species with contrasting patterns of commonness and distribution.

Blambert L1, Mallet B2, Humeau L2, Pailler T2.
Annals of botany.Ann Bot.2016 Mar 4. pii: mcw014. [Epub ahead of print]
BACKGROUNDS AND AIMS: Theory predicts that the long-term persistence of plant populations exposed to size reduction can be threatened by a loss of genetic diversity and increased inbreeding. However, several life-history and ecological traits can influence the response to population size reduction.
PMID 26944785