deoxyribose the sugar characterizing DNA.
dependent differentiation differentiation of an embryonic tissue caused by a stimulus coming from other tissue and dependent on that stimulus. depolymerization the breakdown of an organic compound into two or more molecules of less com- plex structure. derepression an increased synthesis of gene prod- uct accomplished by preventing the interaction of a repressor with the operator portion of the operon in question.
In the case of inducible enzyme systems, the inducer derepresses the operon. A mutation of the regulatory gene that blocks synthesis of the re- pressor or a mutation of the operator gene that ren- ders it insensitive to a normal repressor will also re- sult in derepression. See regulator gene. derived the more recent stages or conditions in an evolutionary lineage; the opposite of primitive. dermatoglyphics the study of the patterns of the ridged skin of the palms, fingers, soles, and toes.
Desferal the trade name for desferrioxamine, an iron chelator. Children with hereditary diseases that cause red blood cells to die at an accelerated pace receive frequent blood transfusions. Eventually their systems become overloaded with iron, and this can damage both heart and liver.
Such children are often fitted with an intravenous Desferal pump. This in- fuses them with the chelator, which leaches the ex- cess iron out of their bodies. See Cooley anemia, tha- lassemia.
desmids green algae that exist as pairs of cells with their cytoplasms joined at an isthmus that contains a single shared nucleus. See Appendix A, Protoctista, Gamophyta; Micrasterias thomasiana. desmin a 51,000-dalton cytoskeletal protein.
Des- min molecules fall into the intermediate filament class and are found in glial and muscle cells. desmosome an intercellular attachment device. It is a discontinuous button-like structure consisting of two dense plaques on the opposing cell surfaces,
separated by an intercellular space about 25 nano- meters wide. On each symmetrical half-desmosome a thin layer of dense material coats the inner leaf of the cell membrane, and bundles of fine cytoplasmic filaments converge upon and terminate in this dense substance. desoxyribonucleic acid an obsolete spelling of de- oxyribonucleic acid found in older literature. destruction box See cyclins. desynapsis the failure of homologous chromo- somes that have synapsed normally during pachy- nema to remain paired during diplonema. Desynap- sis is usually the result of a failure of chiasma formation.
Contrast with asynapsis. detached X an X chromosome formed by the de- taching of the arms of an attached X chromosome (q.v.), generally through crossing over with the Y chromosome. determinant 1. in immunology, the portion of the antigen that is responsible for the specificity of the response and that is recognized by the binding sites of immunoglobulins and antigen-recognizing lym- phocytes. 2. a factor that signals a cell to follow a particular developmental pathway. See cytoplasmic determinant.
determinant cleavages a successive series of cleavages that follow a specific three-dimensional pattern such that with each division, cells are pro- duced, each of which can be shown to serve as the progenitor of a specific type of tissue. In developing mollusc eggs, for example, cell 4d, which is formed at the sixth cleavage, is always the progenitor of all primary mesodermal structures.
determinate inflorescence an inflorescence in which the first flowers to open are at the tip or inner part of the cluster, and the later ones are progres- sively lower or farther out. determination the establishment of a single kind of histogenesis for a part of an embryo, which it will perform irrespective of its subsequent situations. Compare with differentiation. deubiquitinating enzymes a large and heteroge- neous group of cysteine proteases (q.v.) that specifi- cally cleave off polyubiquitin chains from ubiquitin- conjugated proteins or generate ubiquitin monomers from polyubiquitin chains.
These enzymes are thought to have a broad range of substrate specifici- ties and may play a regulatory role in protein ubiqui- tination-related processes. See otu, ubiquitin, ubiqui- tin-proteasome pathway (UPP). deutan See color blindness. deuteranomaly See color blindness. deuteranopia See color blindness. deuterium See hydrogen. deuteron the nucleus of a deuterium atom, con- taining one proton and one neutron.
Deuterostomia one of the two subdivisions of the Bilateria. It contains the echinoderms, the chordates, and a few smaller phyla. The deuterostome egg un- dergoes radial cleavage (q.v.), and the cells produced in early cleavage divisions retain the ability to de- velop into the complete embryo. The blastopore (q.v.) becomes the anus, and the coelom arises as pouches from the primitive gut. Compare with Pro- tostomia. See Appendix A.
deuterotoky parthenogenesis in which both males and females are produced. developer a chemical that serves as a source of re- ducing agents that will distinguish between exposed and unexposed silver halide and convert the exposed halide to metallic silver, thus producing an image on a photographic film. development an orderly sequence of progressive changes resulting in an increased complexity of a bi- ological system. See determination, differentiation, morphogenesis. developmental control genes genes which con- trol the developmental decisions of other genes.
Such genes have been extensively studied in Dro- sophila, Caenorhabditis, Danio, Mus, and Arabidop- sis. See Appendix C, 1978, Lewis; 1980, Nu¨sslein- Volhard and Weischaus; 1981, Chalfie and Sulston; 1983, Bender et al., Scott et al.; 1984, McGinnis et al.; 1986, Tomlinson and Ready, Noll et al.; 1987, Nu¨sslein-Volhard et al.; Struhl, Herr et al.; 1989 Driever and Nu¨sslein-Volh- ard, Zink and Paro; 1990, Malicki et al.; 1993, Mul- lins and Nu¨sslein-Volhard; 1994, Bollag et al.; 1995, Halder et al.; 1996, Dubnau and Struhl, Krizek and Meyerowitz; cell lineage mutants, compartmentaliza- tion, floral identity mutations, gene networking, Hox genes, metamerism, selector genes, T box genes, zy- gotic segmentation mutations. developmental genetics the study of mutations that produce developmental abnormalities in order to gain understanding of how normal genes control growth, form, behavior, etc.