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. 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.