Filial generation

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. Subsequent generations are called F₂, F₃, etc.

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 breeding the parents often 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.

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.

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