Angelman syndrome (AS)
androgenic gland a gland found in most crusta- ceans belonging to the subclass Malacostraca. When implanted into maturing females, the gland brings about masculinization of primary and secondary sex characters.
androgen insensitivity syndrome a condition in which XY individuals develop as normal-appearing, but sterile, females. Spermatogenesis does not occur in the testes, which are generally located inside the abdomen. Also called testicular feminization. See Ap- pendix C, 1988, Brown et al.; androgen receptor, an- drogen receptor gene. androgenote a cell or embryo produced by andro- genesis.
Compare with gynogenote. androgen receptor (AR) a protein belonging to a subfamily of steroid hormone receptors within a larger family of DNA-binding proteins. The human AR is made up of 919 amino acids and is subdivided into three domains. The N-terminal domain has a regulatory function, and the C-terminal domain binds dihydrotestosterone. The central domain, which binds to DNA, contains zinc fingers.
The receptor binds to DNA as a homodimer. See androgen, testos- terone, vitamin D receptor, zinc finger protein. androgen receptor gene a gene symbolized AR that is located on the X chromosome at q12. It con- tains eight exons and is 180,245 bp long. AR en- codes the androgen receptor (q.v.).
Homologous genes occur in the rat and mouse. Mutations in criti- cal portions of AR cause the loss of receptor activity, and this results in abnormalities in sexual phenotype referred to as androgen insensitivity syndrome (q.v.) or testicular feminization.
See Appendix C, 1988, Brown et al. androgynous 1. being neither distinguishably mas- culine nor feminine in appearance or behavior. 2. bearing staminate and pistillate flowers on distinct parts of the same inflorescence. See flower. andromonecy a sexual condition in which plants develop both staminate flowers (that do not develop fruit) and hermaphroditic flowers. androphages “male-specific” bacteriophages that absorb on the surface of F pili.
Examples are MS2, R17, and Qβ (all of which see). See F factor (fertility factor). anemia a disorder characterized by a decrease in hemoglobin per unit volume of blood. In the case of hemolytic anemia, there is a destruction of red blood cells. In the case of hypochromic anemia, there is a reduction in the hemoglobin content of the erythro-
anemophily pollination by the wind. anergy the lack of an expected immune response. aneucentric referring to an aberration generating a chromosome with more than one centromere. aneuploidy the condition in which the chromo- some number of the cells of an individual is not an exact multiple of the typical haploid set for that spe- cies. The nomenclature employs the suffix somic, as the following examples illustrate.
Down syndrome (q.v.) and Turner syndrome (q.v.) are examples of a human trisomic and monosomic, respectively. Nulli- somics result from the loss (2N − 2) and tetrasomics from the gain (2N + 2) of a chromosome pair.
If more than one different chromosome is lost or gained, the condition is described as doubly monosomic (2N − 1−1)ordoublytrisomic(2N+1+1).Earlystudies of aneuploids led to the conclusion that genes car- ried by specific chromosomes controlled morpholog- ical traits. For example, in Datura stramonium (q.v.) extra doses of chromosome G broaden and reduce the seed capsule and increase the size of the spines (see page 26). See Appendix C, 1934, Blakeslee; hy- perploid, hypoploid, symbols used in human cytoge- netics, polyploid. aneurin vitamin B1; more commonly known as thi- amine. aneusomy the condition in which an organism is made up of cells that contain different numbers of chromosomes.
Aneusomy is widespread in flowering plants possessing B chromosomes (q.v.). In animals, the term generally refers to a diploid organism with subpopulations of aneuploid, somatic cells. The term aneusomy has been misused in the recent liter- ature of human cytogenetics to refer to a genetic im- balance within a chromosome pair. For example, an individual heterozygous for a deficiency including one or more genes is hemizygous for those genes on the normal homolog. To call such an individual a segmental aneusomic is confusing, since aneusomy traditionally implies mosaicism. See aneuploidy.
Angelman syndrome (AS) children with this con- dition are hyperactive and are unable to develop normal speech. Because they show impaired motor control and tend to laugh excessively, the condition is sometimes called “happy puppet syndrome.” The British pediatrician Harry Angelman gave the first description of children with the disease in 1965. Later the condition was found to be the result of a deletion in the long arm of chromosome 15. See Prader-Willi syndrome (PWS).
Aneuploidy in the Jimson weed, Datura stramonium. Extra doses of G chromosomes make the seed capsules smaller and broader and their spines larger.
angiosperm a flowering plant. Any species in the Superclass Angiospermae (see Appendix A, Kingdom Plantae) characterized by having seeds enclosed in an ovary. Almost all agriculturally important plants (apart from conifers) belong to the Angiospermae. Angstrom unit a unit of length equal to one ten- thousandth of a micron (10−4 micron; a micron being 10−6 meter); convenient for describing atomic di-mensions; also equivalent to 10−1 nanometers (nm) or 10−10 meter. Abbreviated A, A°, A˚, A˚.U., or A.U. Named in honor of the Swedish physicist Anders Jonas A˚ngstrom.
Animalia the kingdom containing animals (hetero- trophic organisms developing from a blastula). See Appendix A, Kingdom 4; opisthokonta. animal pole that pole of an egg which contains the most cytoplasm and the least yolk. anion a negatively charged ion. Contrast with cation. Aniridia a dominant mutation of the Pax-6 gene located at 11p13, which causes defects in the iris, lens, cornea, and retina of humans.
The Pax-6 gene of humans, the Sey gene of mice and rats, and the ey gene of Drosophila are homologous. See eyeless. anisogamy that mode of sexual reproduction in which one of the sex cells, the egg, is large and non- mobile, whereas the other (the sperm) is small and motile.
In most anisogamous eukaryotes, the centri- ole is paternally inherited. See isogamy, partheno- genesis. anisotropy a directional property of crystals and fibers having a high degree of molecular orientation. Anisotropic substances have different physical prop- erties when tested in different directions.
When a ray of plane polarized light passes through aniso- tropic material, it is split into two rays polarized in mutually perpendicular planes. This property of ani- sotropic material is called birefringence.
Muscle fibers and the metaphase spindle are examples of living materials exhibiting birefringence.
Materials show- ing no birefringence are said to be isotropic. See po- larization microscope. ankylosing spondylitis an arthritic disease result- ing in a stiffening and bending of the spine; inherited as an autosomal dominant with reduced penetrance. Over 90% of patients with this disease carry the B27 HLA antigen. See histocompatibility. ankyrin a protein that binds to β-spectrin as well as to the cytoplasmic domains of a variety of integral membrane proteins, and that is thought to intercon- nect the spectrin-based membrane cytoskeleton and the overlying lipid bilayer. Based on sequence simi- larity, ankyrins have been identified in various tis- sues and cell types from a variety of organisms.
These proteins generally have three structural do- mains: a conserved, N-terminal region containing membrane-binding properties, a highly conserved spectrin-binding region, and a variable, regulatory C- terminal domain. In humans, three forms of ankyrin have been characterized. Ankyrin-1 (also called ankyrin-R) is encoded by the ANK1 gene at chro- mosomal map position 8p11 and expressed in eryth- rocytes and the brain.
Ankyrin-2 (also called an- kyrin-B) is encoded by the ANK2 gene at position 4q25-q27 and expressed primarily in the brain.
A third protein, ankyrin-3 (also known as ankyrin-G), is encoded by the ANK3 gene mapping to 10q21, and alternatively spliced isoforms are expressed in nervous tissue, muscle, and other tissues.
Mutations in the erythrocytic ankyrin gene, ANK1, are associ- ated with hereditary spherocytosis (q.v.). See fu- some, integral protein, spectrin, spectrosome. anlage the embryonic primordium from which a specific part of the organism develops. anneal to subject first to heating then to cooling. In molecular genetics experiments, annealing is used to produce hybrid nucleic acid molecules containing paired strands, each from a different source.
Heating results in the separation of the individual strands of any double-stranded, nucleic-acid helix, and cooling leads to the pairing of any molecules that have seg- ments with complementary base pairs. annidation the phenomenon where a mutant is maintained in a population because it can flourish in an available ecological niche that the parent organ- isms cannot utilize.
A wingless mutant insect, for ex- ample, might be poorly adapted in its ancestral habi- tat but able to live in tunnels and crevices that a winged form could not occupy. annotation See genome annotation. annulate lamellae paired membranes arranged in stacks and possessing annuli resembling those of the nuclear membrane. Annulate lamellae may serve to transfer nuclear material to the cytoplasm by the replication of the nuclear envelope and may be a mechanism for storing gene-derived information to be used for cytoplasmic differentiation during early embryogenesis.
During insect oogenesis, annulate la- mellae occur alongside nurse cell nuclei and germi- nal vesicles, and they are abundant in the ooplasm. annulus a ring. Applied to any of a number of ring-shaped parts of animals and plants. Used in cy- tology to refer to the ring-shaped nuclear pores. anode the positive electrode; the electrode to which negative ions are attracted. Contrast with cathode. anodontia the congenital absence of teeth. Hypo- dontia is currently the preferred term. anonymous DNA a segment of DNA of unknown gene content that has been localized to a specific chromosome.
Anopheles a genus containing about 150 species of mosquitoes, many of which are of medical impor- tance. Africa’s principal malaria vector is A. gam- biae. Other vector species are A. funestus, A. quadri- maculatus, A. atroparvus, A. nili, A. moucheti, and A. pharoensis.
Polytene chromosomes occur in both larval salivary gland cells and adult ovarian nurse cells. Sibling species can often be separated by dif- ferences in the banding patterns of their polytene chromosomes. The genome of A. gambiae has been shown to contain 278 mbp of DNA and about 13,700 genes. See Appendix A, Arthropoda, Insecta, Diptera; Appendix C, 2002, Holt et al.; Appendix E; intron dynamics, ma- laria, mariner elements, Minos element, shotgun se- quencing. anosmia the absence or loss of the sense of smell. Anosmia may be caused by injury to or loss of olfac- tory receptor neurons (q.v.) or by injury to region(s) in the brain or elsewhere where olfactory signals are processed. Anosmia may also result due to defects in any element of the olfaction signaling pathway.
For example, mice and nematodes with defects in G proteins (q.v.) found in olfactory receptor neurons exhibit olfactory and chemosensory defects, respec- tively. Anser anser the Gray Lag goose, a favorite experi- mental organism for students of animal behavior and its hereditary components. antagonist a molecule that bears sufficient struc- tural similarity to a second molecule to compete with that molecule for binding sites on a third mole- cule.
See competition. antagonistic pleiotropy a phenomenon in which alleles (that are detrimental late in life) improve fit- ness earlier in life. antenatal before birth; during pregnancy. antennae the first paired appendages on the head of arthropods. Antennapedia a gene residing at 47.9 on the ge- netic map and within segment 84B of the salivary map of Drosophila melanogaster. The Antp gene is one of a cluster of three genes that specify the type of differentiation that cells in the segments from the