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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.
1 The cross between two different homozygous lines produces an F1 hybrid that is heterozygous; having two alleles, one contributed by each parent and typically one is dominant and the other recessive. 2  Typically, the F1 generation is also phenotypically homogeneous, producing offspring that are all similar to each other. Extremely rare interfamilial hybrids have been known to occur (such as the guineafowl hybrids). 2  No interordinal (between different orders) animal hybrids are known. 3  The third type of hybrid consists of crosses between populations, breeds or cultivars within a single species.