関: first filial generation

WordNet

produced by crossbreeding (同)intercrossed
(genetics) an organism that is the offspring of genetically dissimilar parents or stock; especially offspring produced by breeding plants or animals of different varieties or breeds or species; "a mule is a cross between a horse and a donkey" (同)crossbreed, cross
a composite of mixed origin; "the vice-presidency is a hybrid of administrative and legislative offices"
the 6th letter of the Roman alphabet (同)f

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(動物植の)雑種,(物の)混成物 / 混種語(語源の異なる二つ以上の要素から成る語;たとえばshortageは英語(short)とフランス語(hybridage)の混種語) / 雑種(混成)の

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/06/06 17:14:16」(JST)

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An F1 hybrid (or filial 1 hybrid) is the first filial generation of offspring of distinctly different parental types.^[1] F1 hybrids are used in genetics, and in selective breeding, where it may appear as F1 crossbreed. The term is sometimes written with a subscript, as F₁ hybrid.^[2]^[3] The offspring of distinctly different parental types produce a new, uniform phenotype with a combination of characteristics from the parents. In fish breeding, those parents frequently are two closely related fish species, while in plant and animal genetics the parents usually are two inbred lines. Mules are F1 hybrids between horse and donkey. Today, certain domestic–wild hybrid breeds, such as the Savannah cat, are classified by their filial generation number.

Gregor Mendel focused on patterns of inheritance and the genetic basis for variation. In his cross-pollination experiments involving two true-breeding, or homozygous, parents, Mendel found that the resulting F1 generation were heterozygous and consistent. The offspring showed a combination of the phenotypes from each parent that were genetically dominant. Mendel’s discoveries involving the F1 and F2 generations laid the foundation for modern genetics.

Production of F1 hybrids

In plants

Crossing two genetically different plants produces a hybrid seed. This can happen naturally, and includes hybrids between species (for example, peppermint is a sterile F1 hybrid of watermint and spearmint). In agronomy, the term “F1 hybrid” is usually reserved for agricultural cultivars derived from two parent cultivars. These F1 hybrids are usually created by means of controlled pollination, sometimes by hand-pollination. For annual plants such as tomato and maize, F1 hybrids must be produced each season.

For mass-production of F1 hybrids with uniform phenotype, the parent plants must have predictable genetic effects on the offspring. Inbreeding and selection for uniformity for multiple generations ensures that the parent lines are almost homozygous. The divergence between the (two) parent lines promotes improved growth and yield characteristics in offspring through the phenomenon of heterosis ("hybrid vigour" or "combining ability").

Two populations of breeding stock with desired characteristics are subjected to inbreeding until the homozygosity of the population exceeds a certain level, usually 90% or more. Typically this requires more than ten generations. Thereafter the two strains must be crossed, while avoiding self-fertilization. Normally this is done with plants by deactivating or removing male flowers from one population, taking advantage of time differences between male and female flowering or hand-pollinating.^[4]

In 1960, 99 percent of all corn planted in the United States, 95 percent of sugar beet, 80 percent of spinach, 80 percent of sunflower, 62 percent of broccoli and 60 percent of onions were F1 hybrids. Beans and peas are not commercially hybridized because they are automatic pollinators, and hand-pollination is prohibitively expensive.

F2 hybrid

F2 hybrids, the result of self or cross pollination of F1s, lack the consistency of F1s, though they may retain some desirable traits and can be produced more cheaply, because hand pollination or other interventions are not required. Some seed companies offer F2 seed at less cost, particularly in bedding plants where consistency is less critical.^[5]

In animals

F1 crosses in animals can be between two inbred lines or between two closely related species or subspecies. In such fish as cichlids, the term F1 cross is used for crosses between two different wild-caught individuals that are assumed to be from different genetic lines.^[6]

Advantages

Homogeneity and predictability—The genes of individual plant or animal F1 offspring of homozygous pure lines display limited variation, making their phenotype uniform and therefore attractive for mechanical operations and easing fine population management. Once the characteristics of the cross are known, repeating this cross yields exactly the same result.
Higher performance—As most alleles code for different versions of a protein or enzyme, having two different versions of this allele amounts to having two different versions of the enzyme. This increases the likelihood of an optimal version of the enzyme being present and reduces the likelihood of a genetic defect.

Disadvantages

The main advantage of F1 hybrids in agriculture is also their drawback. When F1 cultivars are used as parents, their offspring (F2 generation) vary greatly from one another. Some F2s are high in homozygous genes, as found in their grandparents, and these will lack hybrid vigour. From the point of view of a commercial seed producer who does not wish customers to produce their own seed, this genetic assortment is a desired characteristic.
Both inbreeding and crossing the ancestral lines of the hybrid are costly, which translates into a much higher price. In general, the higher yield, etc., offsets this disadvantage.
F1 hybrids mature at the same time when raised under the same environmental conditions. They all ripen simultaneously and can be more easily harvested by machine. Traditional cultivars and landraces are often more useful to gardeners because they crop over a longer period of time, avoiding gluts and food shortages.

References

^ Marschall S. Runge and Cam Patterson (editors) (2006). Principles of Molecular Medicine. Humana Press. p. 58. ISBN 978-1-58829-202-5.
^ Peter Abramoff and Robert G. Thomson (1994). Laboratory Outlines in Biology--VI. Macmillan. p. 497. ISBN 978-0-7167-2633-3.
^ William Ernest Castle and Gregor Mendel (1922). Genetics and eugenics: a text-book for students of biology and a reference book for animal and plant breeders. Harvard University Press. p. 101.
^ Hand Pollination
^ Lawrence D. Hills (1987). "F2 and open pollinated varieties". Growing From Seed (The Seed Raising Journal from Thompson & Morgan) 1 (2).
^ "Guide to selecting and breeding high quality cichlids". bigskycichlids.com.

External links

Richard A. Grazzini (1997). "Genetics for Seed Savers". |chapter= ignored (help)
Seeds: The Yearbook of Agriculture 1961. United States Department of Agriculture.

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English Journal

Female Mecp2+/- mice display robust behavioral deficits on two different genetic backgrounds providing a framework for pre-clinical studies.

Samaco RC, McGraw CM, Ward CS, Sun Y, Neul JL, Zoghbi HY.AbstractRett syndrome (RTT) is an X-linked neurological disorder caused by mutations in the gene encoding the transcriptional modulator methyl-CpG-binding protein 2 (MeCP2). Typical RTT primarily affects girls and is characterized by a brief period of apparently normal development followed by the loss of purposeful hand skills and language, the onset of anxiety, hand stereotypies, autistic features, seizures and autonomic dysfunction. Mecp2 mouse models have extensively been studied to demonstrate the functional link between MeCP2 dysfunction and RTT pathogenesis. However, the majority of studies have focused primarily on the molecular and behavioral consequences of the complete absence of MeCP2 in male mice. Studies of female Mecp2(+/-) mice have been limited because of potential phenotypic variability due to X chromosome inactivation effects. To determine whether reproducible and reliable phenotypes can be detected Mecp2(+/-) mice, we analyzed Mecp2(+/-) mice of two different F1 hybrid isogenic backgrounds and at young and old ages using several neurobehavioral and physiological assays. Here, we report a multitude of phenotypes in female Mecp2(+/-) mice, some presenting as early as 5 weeks of life. We demonstrate that Mecp2(+/-) mice recapitulate several aspects of typical RTT and show that mosaic expression of MeCP2 does not preclude the use of female mice in behavioral and molecular studies. Importantly, we uncover several behavioral abnormalities that are present in two genetic backgrounds and report on phenotypes that are unique to one background. These findings provide a framework for pre-clinical studies aimed at improving the constellation of phenotypes in a mouse model of RTT.
Human molecular genetics.Hum Mol Genet.2013 Jan 1;22(1):96-109. doi: 10.1093/hmg/dds406. Epub 2012 Oct 1.
Rett syndrome (RTT) is an X-linked neurological disorder caused by mutations in the gene encoding the transcriptional modulator methyl-CpG-binding protein 2 (MeCP2). Typical RTT primarily affects girls and is characterized by a brief period of apparently normal development followed by the loss of pu
PMID 23026749

Transmission ratio distortion of molecular markers in a doubled haploid population originated from a natural hybrid between Osmunda japonica and O. lancea.

Yatabe-Kakugawa Y, Tsutsumi C, Hirayama Y, Tsuneki S, Murakami N, Kato M.SourceBotanical Gardens, Graduate School of Science, The University of Tokyo, 3-7-1 Hakusan, Bunkyo-ku, Tokyo, 112-0001, Japan, ykakugawa@ns.bg.s.u-tokyo.ac.jp.
Journal of plant research.J Plant Res.2012 Dec 6. [Epub ahead of print]
In ferns, intra-gametophytic selfing occurs as a mode of reproduction where two gametes from the same gametophyte form a completely homozygous sporophyte. Intra-gametophytic selfing is considered to be prevented by lethal or deleterious recessive genes in several diploid species. In order to investi
PMID 23224293

Tissue-specific relationship of S-adenosylhomocysteine with allele-specific H19/Igf2 methylation and imprinting in mice with hyperhomocysteinemia.

Glier MB, Ngai YF, Sulistyoningrum DC, Aleliunas RE, Bottiglieri T, Devlin AM.SourceDepartment of Pathology and Laboratory Medicine; University of British Columbia; Child & Family Research Institute; Vancouver, BC Canada.
Epigenetics : official journal of the DNA Methylation Society.Epigenetics.2012 Dec 5;8(1). [Epub ahead of print]
DNA methylation is linked to homocysteine metabolism through the generation of S-adenosylmethionine (AdoMet) and S-Adenosylhomocysteine (AdoHcy). The ratio of AdoMet/AdoHcy is often considered an indicator of tissue methylation capacity. The goal of this study is to determine the relationship of tis
PMID 23221482