frizzle,” with more normal curly feathers. Frizzle feather keratin shows a poorly ordered crystalline structure, and its amino acid composition is ab- normal. fructification 1. a reproductive organ or fruiting body. 2. the generation of fruit or spore-producing structures by plants. fructose a six-carbon hexose sometimes called lev- ulose. It is a component of sucrose.
fructose intolerance a disorder of carbohydrate metabolism inherited as an autosomal recessive. Pa- tients lack fructose-1,6-diphosphatase. Symptoms disappear if dietary fructose is restricted. fruit the ripened ovary of the flower that encloses the seeds. fruit fly See Drosophila. FSH follicle-stimulating hormone (q.v.). F− strain Escherichia coli behaving as recipients during unidirectional genetic transfer. F+ strain Escherichia coli behaving as donors during unidirectional genetic transfer. See F factor. F test See analysis of variance. Fugu rubripes Takifugu rubripes (q.v.).
functional cloning in human genetics, the identi- fication of the gene responsible for a disease from a knowledge of the underlying molecular defect. If the protein encoded by the gene is known, it is often possible to isolate the appropriate mRNAs and to use them, or cDNAs derived from them, as probes for the gene. This was the first method used success- fully to clone genes responsible for certain hereditary diseases, such as sickle cell anemia, Tay-Sachs dis- ease, and phenylketonuria. Contrast with positional cloning. See cDNA, hereditary disease, mRNA, probe. fundamentalism a conservative religious ideology that holds the origin and diversity of life is by divine creation, based upon a literal interpretation of the biblical account of Genesis. See creationism.
fundamental theorem of natural selection a the- orem developed by R. A. Fisher according to which the increase in fitness of a population at any given time is directly proportional to the genetic variance in fitness of its members. Fungi the kingdom that contains yeasts, molds, smuts, rusts, mushrooms, and other saprophytes. These organisms are placed at the bottom of most phylogenies that show the evolution of the eukaryo- tic kingdoms. Their primitive characters include mi- tochondria with plate-shaped cristae, a Golgi made up of individual dictyosomes, and mitosis with an endonuclear spindle. Fungi cannot perform endocy- tosis, and they lack undullipodia and centrioles. They reproduce by forming spores. See Appendix A, Kingdom 3; opisthokonta. funiculus the plant stalk bearing on ovule. fused gene See fusion gene.
fused protein a hybrid protein molecule produced when a gene of interest is inserted by recombinant DNA techniques into a recipient plasmid and dis- places the stop codon for a plasmid gene. The fused protein begins at the amino end with a portion of the plasmid protein sequence and ends with the pro- tein of interest. Compare with polyprotein. See Ap- pendix C, 1970, Yourno et al. fushi tarazu (ftz) one of the pair rule selector genes of Drosophila.
The name means segment defi- cient in Japanese. The ftz gene is located at 3-47.5, within the Antennapedia complex, and it is first ex- pressed within 7 vertical stripes of cells in the early embryo. It has later functions during metamorphosis when it specifies the identities of individual neurons in the developing central nervous system. FTZ, the protein encoded by ftz, contains a PEST sequence (q.v.) and a homeobox (q.v.). FTZ functions as an activator of the transcription of segment polarity genes such as engrailed.
But FTZ can also function as a suppressor of transcription for genes such as wing- less. See zygotic segmentation mutants. fusidic acid an antibiotic that prevents translation by interfering with elongation factor G. fusion gene 1. a hybrid gene, composed of parts of two other genes, arising from deletion of a chro- mosomal segment between two linked genes or by unequal crossing over. Hemoglobin Lepore (q.v.) is an example of such a fused gene. See cone pigment genes (CPGs), Philadelphia chromosome. 2. a labora- tory construct consisting of regulatory elements from one gene ligated to the structural elements of another. Transgenic animals (q.v.) often carry fused genes.
fusome a cytoplasmic organelle that is required for the proper formation of germ line syncytia during gametogenesis in both male and female insects. fusome arises from endoplasmic reticulum that tra- verses the ring canals (q.v.) formed during successive cycles of incomplete mitotic germ cell divisions. After each division, a plug of fusomal material accu- mulates in each newly-formed ring canal. This mate- rial then fuses with the fusome(s) formed from the previous division(s), and ultimately a mature, branched structure called a polyfusome is produced. The polyfusome entry illustrates how this structure directs the pattern of cystocyte interconnections by anchoring one pole of each mitotic spindle, thus ori- enting the plane of cell division. The first Drosphila
mutant shown to have fragmented fusomes was called otu because it formed ovarian tumors made up of hun- dreds of cells, most of which were not connected by ring canals and which never differentiated into either oocytes or nurse cells. Mitotic effectors such as cyclin A (q.v.) have been shown to bind transiently with fu- somes during G2 and prophase, and this suggests that the fusomal system plays a role in the timing, syn- chronization, and eventual cessation of cystocyte divi- sions (q.v.). Among the other components identified in fusomes are alpha and beta spectrins, ankyrin, an adducin-like protein, dynein, and a protein encoded by the bag of marbles gene. Mutations in this gene also produce ovarian tumors. See adducin, bag of marbles (bam), hu-li tai shao (hts).