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An F1 hybrid (or filial 1 hybrid) is the first filial generation of offspring of distinctly different parental types. 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.
F1 Savannahs can be as high as 75% serval. All 75% F1s (technically a backcross, or BC1) are the offspring of a 50% F1 (true F1) female bred back to a serval. Cases of 87.5% F1 (technically BC2) Savannah cats are known, but fertility is questionable at those percentage Serval levels.