- a cross between an individual of the first filial generation (F1) and one of the parental types
Source: Noland, George B. 1983. General Biology, 11th Edition. St. Louis, MO. C. V. Mosby
- A cross between an animal that is heterozygous for alleles obtained from two parental strains and a second animal from one of those parental strains. Also used to describe the breeding protocol of an outcross followed by a backcross.