also developed favism. Various compounds in fava beans are enzymatically hydrolyzed to quinones, which generate oxygen radicals. Red blood cells de- ficient in glucose-6-phosphate dehydrogenase (q.v.) have a marked sensitivity to oxidating agents and lyse when oxygen radicals are abundant. The toxic properties of fava beans have been known for centu- ries in Mediterranean cultures where glucose-6- phosphate dehydrogenase deficiency (q.v.) is a com- mon hereditary disease. Favism generally occurs in males hemizygous for the A− or M alleles of the Gd gene.
FBNI See fibrillin. F+ cell a bacterial cell possessing a fertility (F) fac- tor extrachromosomally in a plasmid. An F+ cell can donate the F factor to an F− cell during conjugation. If the F factor integrates into the bacterial chromo- some, the cell becomes an Hfr (q.v.), capable of transferring chromosomal genes. See F factor. F− cell a bacterial cell devoid of an F factor and that therefore acts only as a recipient (“female”) in bacterial conjugation.
Fc fragment that crystallizable fragment (hence the name) of a papain-digested immunoglobulin molecule that contains only portions of two heavy chains and no antibody binding sites. This fragment does, however, bind complement and is responsible for the binding of immunoglobulin to various types of cells in a non-antigen-specific manner. See immu- noglobulin. Fc receptor a cell-surface component of many cells of the immune system responsible for binding the Fc portion of immunoglobulin molecules. F-duction See sexduction. fecundity potential fertility or the capability of re- peated fertilization. Specifically, the term refers to the quantity of gametes, generally eggs, produced per individual over a defined period of time.
See fer- tility. feedback the influence of the result of a process upon the functioning of the process. feedback inhibition end product inhibition (q.v.). feeder cells irradiated cells, capable of metaboliz- ing but not of dividing, that are added to culture me- dia to help support the growth of unirradiated cells. feline leukemia virus an oncogenic RNA virus. Felis catus the house cat, a domesticated version of the African wild cat Felis silvestris. Its haploid chromosome number is 19, and about 600 genes have been mapped. Of all the non-primate species for which DNA sequences are available, the cat’s ge- nome is the closest to the human. Cats and humans have about 200 disease-associated genes that are or- thologs. The complete 17,009 bp sequence is known for the mtDNA of cats. See Appendix A, Animalia, Eutheria, Carnivora; Appendix E; cat for a listing of breeds, tortoiseshell cat.
female carrier in human pedigrees, a woman who is heterozygous for a recessive, X-chromosomal gene. female gonadal dysgenesis Turner syndrome (q.v.). female pronucleus the haploid nucleus of a fe- male gamete, which functions in syngamy. female-sterile mutation one of a class of muta- tions that cause female sterility generally because of a developmental block during oogenesis. Recessive female-sterile mutations are common in Drosophila melanogaster and Bombyx mori. Dominant female- steriles are much rarer. female symbol O the zodiac sign for Venus, the goddess of love and beauty in Roman mythology. The sign represents a looking glass. F-episome See fertility factor. F′-episome an F-episome carrying a genetically recognizable fragment of bacterial chromosome. feral pertaining to formerly domesticated animals now living in a wild state. fermentation an energy-yielding enzymatic break- down of sugar molecules that takes place in bacteria and yeasts under anaerobic conditions. See Appendix C, 1861, Pasteur. ferritin an iron storage protein found in the liver and spleen, containing up to 20% of its weight in the form of iron.
It consists of a protein component (apoferritin) and colloidal micelles of ferric hydrox- ide-ferric phosphate. Ferritin is often conjugated to proteins such as immunoglobulins, thus enabling their locations within tissues to be determined in electron micrographs due to the great electron scat- tering property of the iron atoms. See Appendix C, 1959, Singer. ferritin-labeled antibodies See ferritin. fertile crescent a crescent-shaped region in the Middle East that in ancient times stretched along the eastern shore of the Mediterranean Sea through the valleys of the Tigris and Euphrates Rivers to the Per- sian Gulf. This region was a very early center of agri- culture and was the place where most of the major domesticated animals and several of the world’s crops were first farmed (9,000 to 4,500 B.C.).
fertility the productivity of an individual or popu- lation in terms of generating viable offspring. The term is often used to refer to the number of off- spring generated by a female during her reproduc- tive period. In human genetics, the term effective fer- tility is used to refer to the mean number of offspring produced by individuals suffering from a hereditary disease as compared to the mean number of off- spring produced by individuals free from the disease, but otherwise very similar. Effective fertility thus gives an indication of the selective disadvantage of the disease. Compare with fecundity. fertility factor F factor (q.v.).
fertility restorer a dominant nuclear gene in corn that nullifies the effect of a cytoplasmic male-steril- ity factor. fertilization the union of two gametes to produce a zygote. See Appendix C, 1769, Spallanzani; 1875, Hertwig; double fertilization, syngamy. fertilization cone a conical projection protruded from the surface of certain eggs at the point of con- tact with the fertilizing sperm. fertilization membrane a membrane that grows outward from the point of contact of the egg and sperm and rapidly covers the surface of the egg. fertilizin a substance secreted by the ovum of some species, that attracts sperm of the same spe- cies. fetus (alternative spelling, foetus) a post-embry- onic, unborn or unhatched vertebrate that has devel- oped to a stage where its major body parts resemble those of the mature animal. The term is usually ap- plied to viviparous (q.v.) animals. In humans, a fetus is identified from approximately the eighth week of gestation until birth.
Determination of the legal and moral status of a human fetus is a major area of de- bate in ethics, law, and public policy. See embryo, gestation period. Feulgen-positive stained by the Feulgen proce- dure and therefore containing DNA. Feulgen procedure a cytochemical test that uti- lizes the Schiff reagent (q.v.) as a stain and is specific for DNA. See Appendix C, 1924, Feulgen and Ros- senbeck; 1950, Swift; 1951, Chiba; 1959, Che`vre- mont et al. F factor (fertility factor) a supernumerary sex chromosome, symbolized by F, that determines the sex of E. coli. In the presence of the F episome, the bacterium functions as a male. F is a circular DNA molecule made up of about 94,000 base pairs, about 2.5% the amount in the E. coli chromosome. About one-third of the genes in the F chromosome are in- volved in the transfer of male genetic material to the female, including the production of the F-pilus.