Filial generation (F1) Denotes the different generations involved in breeding experiments. F1 is the first filial or filial-one generation i.e. the progeny after mating or genetically crossing two types of parents with different genotypes or phenotypes (the parents are known as the P generation); F2 is the second filial or filial-two generation, i.e. the progeny of self-fertile or intercrossing F1 individuals and so on. Members of this generation are two generations remote from the original parent generation.