F 1. Wright’s inbreeding coefficient 2. fluorine. 3. Fahrenheit. 4. fertility factor. F1 first filial generation; the offspring resulting from the first experimental crossing of plants or ani- mals. The parental generation with which the ge- netic experiment starts is referred to as P1 (q.v.). See Appendix C, 1900, Bateson. F2 the progeny produced by intercrossing or self- fertilization of F1 individuals. Fab that fragment of a papain-digested immuno- globulin molecule that bears a single antigen-binding site and contains one intact light chain and a portion of one heavy chain. See immunoglobulin. F(ab)2 fragment that fragment of a pepsin-digested immunoglobulin molecule that contains portions of two heavy chains and two intact light chains and bears two antigen-binding sites. See immunoglobulin. Fabry disease a hereditary disease of glycosphin- golipid metabolism in humans. The disease results from a mutation in the X-linked gene that codes for lysosomal alpha galactosidase A (q.v.).
The enzyme defect causes the accumulation of glycosphingolipids in lysosomes of blood vessels and leads to vascular malfunctions. Fabry disease can be detected in utero by demonstration of a lack of alpha galactosidase A activity in amniocytes of XY fetuses. Heterozygous females can be documented by cloning cultured skin fibroblasts followed by the demonstration of two cell populations, one normal and one lacking enzyme activity (see dosage compensation). Hemizygotes survive to sexual maturity, so the mutation is trans- mitted by both heterozygotes and hemizygotes. Prevalence 1/40,000 males. The disease was de- scribed in 1898 by the German dermatologist Johan- nes Fabry. An English surgeon, William Anderson, discovered it independently in the same year. The condition is most commonly referred to as Fabry dis- ease but sometimes as Fabry-Anderson or Anderson- Fabry disease or syndrome. facet ommatidium (q.v.). factor 8 See antihemophilic factor.
factor 9 See plasma thromboplastin component. factorial a continuing product of factors, calling for the multiplication together of all the integers from one to the given number. Factorial four means 1×2×3×4=24. The usual factorial symbol is an exclamation point (!) following the largest number in the series. Thus factorial four is written 4! facultative having the capacity to live under more than one specific set of environmental conditions. For example, a facultative parasite need not live as a parasite (if another food source is available). A facul- tative apomict may reproduce sexually or asexually depending upon environmental conditions.
Compare with obligate. facultative heterochromatin See heterochromatin. FAD flavin adenine dinucleotide, a coenzyme (q.v.). Fagus sylvatica the European beech tree. Fahrenholz rule the hypothesis that in groups of permanent parasites the classification of the parasites corresponds directly with the natural relationships of their hosts. For example, closely related species of mammals are generally parasitized by closely related species of lice. The rule is based on the assumption that the intimate associations of parasites with their hosts necessitate that they evolve and speciate in harmony with their hosts. As a result of this coevo- lution, speciation and patterns of divergence in host taxa are paralleled by their parasites. An underlying assumption of the Fahrenholz rule is that there is no dispersal of parasites between unrelated hosts. The eponym honors the German entomologist, Heinrich Fahrenholz, who formulated the concept.
See re- source tracking. falciparum malaria See malaria. fallout the radioisotopes generated by nuclear weapons that are carried aloft and eventually fall to the earth’s surface and contaminate it. false negative, false positive See statistical errors. familial Down syndrome See translocation Down syndrome. familial amyotrophic lateral sclerosis (FALS) the hereditary form of amyotrophic lateral sclerosis (ALS) (q.v.). Five to ten percent of the cases of ALS are hereditary and about 20% of these are due to SOD mutations. See superoxide dismutase.
Familial hypercholesterolemia (FH)
familial hypercholesterolemia (FH) a human he- reditary disease characterized by an elevation in the plasma concentration of low-density lipoproteins (LDLs). FH is inherited as an autosomal dominant, and the gene responsible resides on the short arm of chromosome 19 at region 13.2-3. The prevalence of heterozygotes is about 1/500 among American, Eu- ropean, and Japanese populations, and this makes FH among the most common hereditary diseases.
Homozygotes are rare (1 per million in the U.S.A.). The gene is 45 kilobase pairs long and contains 18 exons that encode the low-density lipoprotein re- ceptor (LDLR).
This glycoprotein is made up of 839 amino acids, which are grouped into five domains. These are (1) the ligand-binding domain, (2) the domain showing homology to the precursor of the epidermal growth factor (q.v.), (3) the domain con- taining bound chains of carbohydrates, (4) the trans- membrane domain, and (5) the cytoplasmic domain. The first domain is negatively charged, and it binds to the positively charged LDL particle. The second is essential for the normal recycling of the receptors. The third stabilizes the receptor. The fourth con- tains hydrophobic amino acids, and it spans the plasma membrane and anchors the LDLR to the cell.
The fifth is necessary for clustering the recep- tors into coated pits. There is a direct relationship between the structural domains and exon sequences. For example, domain 2 is encoded by exons 7-14 and domain 5 by exons 17 and 18. Mutations of the LDLR gene result from insertions, deletions, and missense or nonsense mutations. Most mutations pre- vent the synthesis of LDLRs. The second most com- mon mutant class generates LDLRs that cannot exit the endoplasmic reticulum. In a third mutant class LDLRs are transported to the cell surface, but can- not bind LDL particles.
Finally, there is a rare group of mutant LDLRs that can bind LDL particles, but cannot cluster into coated pits. In most heterozy- gotes, receptor activity is one-half normal and in homozygotes LDLRs are absent. Deficient receptor- mediated endocytosis (q.v.) causes LDLs to accumu- late in the plasma. Cholesterol is deposited on arte- rial walls and atherosclerosis results.
The disease is far more serious in homozygotes than in heterozy- gotes. See Appendix C, 1975, Goldstein and Brown; plasma lipoproteins, WHHL rabbit. family 1. in taxonomy, a cluster of related genera. 2. a set of parents (mother and father, sire and dam, etc.) together with their children (progeny, off- spring) constitutes a nuclear family; an extended fam- ily could include half-sibs, aunts, uncles, grandpar- ents, and/or other relatives. 3. gene family. See multigene family. family selection artificial selection of an individu- al(s) to participate in mating(s) based on the merits of other members of the same family exclusive of parents and ancestors (e.g., full sibs or half sibs). Fanconi anemia the first inherited disease in which hereditary chromosome fragility was estab- lished. The disease is characterized by a pronounced reduction in the number of erythrocytes, all types of white blood cells, and platelets in the circulating blood. Chromosome aberrations are common and usually involve nonhomologous chromosomes. In the Bloom syndrome (q.v.), most chromosome inter- changes are between homologous chromosomes.
The disease may result from a defect in the transport of enzymes functioning in DNA repair from cyto- plasm to nucleus. fast component 1. in reassociation kinetics, the first components to renature, containing highly re- petitive DNA. 2. in electrophoresis, the molecules that move farthest in a given time from the origin. fast green an acidic dye used in cytochemistry. The structure is shown on page 157. fat a glycerol ester of fatty acids. Glycerol tripalmi- tate may be taken as an example: fat body the adipose tissue found in larval and adult insects. These organs behave in many ways like the livers of vertebrates.
The fat body is involved in the metabolism of glycogen and fats. It synthesizes and secretes into the hemolymph proteins such as vitellogenin (q.v.) which are taken up by the oocyte. The fat body responds to different infections by syn- thesizing and secreting peptides with antifungal properties like drosomycin or antimicrobial proper- ties like diptericin. See innate immunity. fate map a map of an embryo in an early stage of development that indicates the various regions whose prospective significance has been established by marking methods.
fatty acid an acid present in lipids, varying in car- bon content from C2 to C34. Palmitic acid may be taken as an example: CH3(CH2)14COOH. fauna the animal life in a given region or period of time. favism a hemolytic response to the consumption of beans produced by Vicia faba (q.v.). Breast-fed babies whose mothers had ingested fava beans have