F0 Generation The initial parent generation in a multi-generation reproduction study. F1 Generation The first filial generation (offspring) in a multi-generation reproduction study.  It is produced by breeding individuals of the F0 generation. F2 Generation The second filial generation (offspring) in a multi-generation reproduction study.  It is produced by breeding individuals of the F1 generation. FDA Food And Drug Administration.  A federal agency responsible for the safety evaluation of drugs, cosmetics, food additives, and medical devices. Femtogram (fg) An extremely minute quantity, 1x10-15 gram. Fetus The unborn offspring in the postembryonic period, after major structures have been outlined.  In humans this occurs from 8-9 weeks after conception until birth. Fibrosis The formation of scar tissue in an organ, generally by replacement of functional organ cells by non-functional fibrous tissue. FIFRA Federal Insecticide, Fungicide, and Rodenticide Act.  A federal law, administered by the EPA, to evaluate and register pesticides.