Fetotoxic: Causing toxic, potentially lethal effects to the developing fetus.
Fibrosarcoma: A malignant tumour arising from connective tissue (see 'tumour').
First Pass Metabolism: rapid uptake and metabolism of an agent by the intestine or the liver, immediately after enteric absorption and before it reaches the systemic circulation.
Fluorescence In-Situ Hybridisation (FISH): A technique that allows individual chromosomes and their centromeres to be visualised in cells.
Forestomach: (See glandular stomach).
Free Radicals: any molecular species capable of independent existence that contains an unpaired electron in an atomic orbital. Many radicals are unstable and highly reactive.
Full gene sequence: the complete order of bases in a gene. This order determines which protein a gene will produce.