Grading - Grading

Japanese: 累進交雑 - るいしんこうざつ（英語表記）grading

This breeding method, also known as noble breeding, is often used to genetically improve unimproved livestock in areas where livestock farming is underdeveloped. A male of an improved species is introduced and crossed with a female of a native species to produce a first generation hybrid, which is then crossed again with a male of an improved species, and the next generation is crossed with an improved species. This method allows the individual to become closer to the improved species with each generation. In the first generation of hybrids, 50% of the genes of the individual are from the improved species, but theoretically, 75% of the genes of a second hybrid and 88% of the genes of a third hybrid will be from the improved species.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

畜産後進地の未改良の家畜を遺伝的に改良する場合にしばしば用いられる交配法で，貴化ともいう。改良種の雄を導入して，在来の品種の雌に交雑して生まれた雑種第1代の雌に，再度改良種の雄を交配し，さらにその次代にも改良種を交配するという方法で，これにより代を重ねるごとに改良種に近づけることができる。雑種第1代ではその個体の遺伝子の50％が改良種のものであるが，理論的には2回雑種では75％，3回雑種では88％が改良種の遺伝子となる。

出典　株式会社平凡社世界大百科事典第２版について　情報

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