C3 carbon fixation pathway A metabolic pathway, characteristic of many plants, in which, during carbon fixation, 3-phosphoglycerate is the first stable intermediate organic compound into which carbon dioxide is converted (3-phosphoglycerate contains three carbon atoms, hence the name C3). The initial product of this pathway is an extremely unstable six-carbon intermediate that instantly splits into 3-phosphoglycerate. See: Calvin cycle.
cabinet of curiosities In Renaissance Europe, a private collection of remarkable or unusual objects, which were typically, but not exclusively of natural origin. MORE INFORMATION
caconym /KAK-ə-nim/ A taxonomic name considered bad for linguistic reasons.
Caenorhabditis elegans /see-no-rab-DĪT-əs EL-ə-gəns/ A nematode much used in biological research, particularly in the field of developmental genetics. Because it is transparent, every cell in its body can be seen. Adults have just 816 cells (302 are neurons). The fate of every cell at every stage of development is known. PICTURE
calcareous /kal-KARE-ee-əs/ Containing, or composed of, calcium carbonate.
calcite /KAL-sight/ A form of calcium carbonate.
calcium (Ca) /KAL-see-əm/ Silver-white metallic element. Atomic weight 40.08; atomic number 20. Vertebrates require relatively large amounts of calcium for the production and maintenance of bone. It is also essential to the function of nerves and muscles, and is a necessary cofactor for the enzymes involved in blood clotting and a variety of other bodily processes. The thyroid hormone calcitonin reduces, and parathyroid hormone increases, blood calcium levels.
calcium carbonate /KAL-see-əm CARB-ə-nate/ A white compound (CaCO₃) occurring naturally as chalk, limestone, and marble. MORE INFORMATION
calcium phosphate /KAL-see-əm FOSS-fate/ The compound making up 85 percent of the mineral content of bone. It also makes up three-quarters of the ash remaining after cremation.
calico cat (British: tortoiseshell-and-white cat) /KAL-ə-koe/ A tortoiseshell cat with white spots. These cats, which are almost exclusively female, have a patchy coloration due to random inactivation of different X chromosomes in different somatic cell lines very early in development (the primary coat color locus in cats is on the X chromosome). PICTURE OF CALICO CAT
calorie (cal) /KAL-er-ee/ The amount of heat needed to raise one gram of water from 14.5˚ to 15.5˚C at a pressure of one atmosphere.
Calvin cycle (also Calvin-Benson cycle or dark reaction) /KAL-vin, BEN-sən/ A series of biochemical reactions taking place in the stroma of the chloroplasts of those plants using the C3 carbon fixation pathway. RuBisCO is the key enzyme of the Calvin cycle. DIAGRAM OF CALVIN CYCLE
calyx /KAL-iks/ The whorl of sepals that encloses a bud and subsequently embraces the base of an open flower.
camera eye /KAM-er-ə/ An eye with a focusable lens.
Cambrian Period (Є) /KAM-bree-ən/ The most ancient (~543 to 488 mya) period of the Paleozoic Era. Geologist Adam Sedgwick based the name on Cambria, which is the Latin name of Wales, where he discovered the first known Cambrian deposits. It was during the Cambrian that the various invertebrate phyla first became abundant as fossils. PICTURE | GEOLOGIC TIME SCALE
cAMP Cyclic adenosine monophosphate (cyclic AMP or cyclic 3',5'-adenosine monophosphate), a diffusable signaling molecule important in many biological processes. cAMP is synthesized from adenosine triphosphate (ATP) by adenylyl cyclase. cAMP decomposition into AMP is catalyzed by phosphodiesterase. cAMP is a "second messenger." That is, it is an signaling molecule that carries a signal of extracellular origin to some site within the cell. Generally, such signals originate from a hormone that is itself too large to enter the cell.
Canadian Shield A broad region of Precambrian rock covering most of Canada. Originating from the ancient continent of Laurentia, it formed the center around which the remainder of the North American continent formed. SEE LOCATION OF CANADIAN SHIELD
canalization /KAN-ə-lie-ZAY-shən/ A tendency to follow a particular developmental pathway despite the effect of mutation or the environment.
cancer /KAN-sir/ A sarcoma or carcinoma; malignant tumor or neoplasm.
canid /KAN-əd, KANE-/ (1) a member of the family Canidae; a dog; (2) pertaining to the family Canidae.
Canidae /KAN-ə-DEE/ The mammalian family that contains dogs and other doglike animals.
canine /KAY-nine/ (1) of, pertaining to, or like dogs; (2) a pointed tooth between the incisors and premolars; in mammalian predators the canines are usually elongated and function in seizing and piercing prey.
canopy /KAN-ə-pee/ The upper level of a forest, composed of the leafy upper branches of the trees.
capillaries The microscopic vessels connecting the arterial system with the venous system.
capillary array An apparatus, composed of an array of gel-filled silica capillaries, used to separate DNA fragments for sequencing. The capillaries' small diameter allows application of more intense electric fields, which results in separations that are much faster than separations using slab gels.
carapace /CARE-ə-pace/ n. The dorsal section of an exoskeleton or shell in various types of animals, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles. Compare: plastron.
carbohydrate /KARB-ō-HĪ-drates/ n. Biochemical compounds such as sugars, starches, and, chitin. They fall into three main classes, monosaccharoses, disaccharoses, and polysaccharoses. They are called carbohydrates because they (1) always contain carbon; (2) always contain hydrogen and oxygen in a two to one ratio (the same ratio as in water). DIAGRAM
carbon (C) A nonmetallic chemical element. Atomic number 6, atomic weight 12.0111. All organic compounds contain carbon, together, most commonly, with hydrogen, oxygen, and nitrogen. PERIODIC TABLE
Carbon-14 (14C also radiocarbon) n. A radioactive isotope of carbon used in radiocarbon dating. Carbon-14 is the rarest of the three carbon isotopes (carbon-12, carbon-13, and carbon-14). Approximately one part per trillion of atmospheric carbon is carbon-14.
carbon cycle n. A cycle composed of two primary processes, photosynthesis and respiration. Photosynthesis produces oxygen and glucose from carbon dioxide and water. Respiration reverses this by creating carbon dioxide and water from glucose and oxygen. See: respiration.
carbon dioxide (CO₂) /dī-AWK-sīd/ n. A colorless, acid-tasting gas produced by all animals; one of the major greenhouse gases. The body eliminates carbon dioxide in exhaled air, urine, and perspiration. Carbon dioxide is essential to all plants, which assimilate it into organic material by photosynthesis. Plants release oxygen as a by-product of this process.
Carboniferous Period (C) /kar-bə-NIF-er-əs/ (~359 to 299 mya) n. The fifth period of the Paleozoic Era. In the United States the Carboniferous is broken into the Mississippian (~359 to 318 mya) and Pennsylvanian (~318 to 299 mya) epochs. The Carboniferous is characterized by low sea levels, extensive glaciation, and heavy forestation, which resulted in the deposition of the coal deposits that give the period its name. PICTURE
carboxyl group (COOH or CO₂H) /kar-BOX-əl/ n. A carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl group. A carboxyl group is present in carboxylic acids, including amino acids. MOLECULAR STRUCTURE
carboxyl terminal (C-terminal or C-terminus) n. The peptide chain end carrying the free alpha carboxyl group of the last amino acid. The sequence of a peptide is normally written with the C-terminus to the right.
carcinogen /kar-SIN-ə-jen/ n. An agent causing cancer.
carcinoma n. A malignant tumor enclosed in connective tissue; tends to infiltrate and metastasize.
cardiac /KARD-ee-ack/ adj. Of, or relating to, or toward the heart.
cardiovascular /KARD-ee-ō-VASK-yə-lər/ adj. Pertaining to the heart and blood vessels.
caries /KARE-eez/ n. Decay and disintegration of bone or tooth; associated with inflammation and the formation of abscesses in the surrounding tissues or periosteum. Tooth caries is commonly known as tooth decay. Bone caries is usually tubercular.
carnivorous /kar-NIV-ə-rəs/ adj. Preying on animals; eating meat — carnivore /KARN-ə-vore/ n.
carpus n. The bones of the wrist taken as a whole. SEE PICTURE
carrier protein (also transport protein) n. A protein that transports a specific enzyme across a biological membrane during facilitated diffusion. It has a binding site that is specific for the particular enzyme it transports.
carrying capacity n. The maximum population density that can be sustained by a particular type of environment.
cartilaginous /KART-ə-LAJ-ə-nəs/ adj. Composed of cartilage.
catabolic pathways /kat-ə-BAWL-ick/ Metabolic processes in which complex molecules are broken down into simpler ones.
catabolism /kə-TAB-bə-liz-əm/ The production of simpler molecules from more complex ones; the products of catabolism are either excreted or used as components in the construction of new, more complex molecules — catabolic /kat-ə-BAWL-ick/ See: anabolism
catabolite /kə-TAB-bə-lite/ A product of a catabolic process.
catalysis /kə-TAL-ə-səs/ The speeding of a chemical reaction by a catalyst.
catalyst /KAT-ə-list/ A molecule that increases the speed of a chemical reaction without being consumed by the reaction.
catalytic /KAT-ə-LIT-ik/ Causing or involving catalysis.
catalyze (British catalyse) /KAT-ə-lize/ To a speed chemical reaction with a catalyst.
catarrhine primates /KAT-ə-rine/ Old World monkeys, apes, and human beings.
catheter /KATH-ə-ter/ A tube for introducing liquids into, or extracting them from, the body.
catheterization (British: catheterisation) /CATH-ə-ter-eye-ZAY-shən/ State of being fitted with a catheter.
cation A positively charged ion.
caudad /CAW-dad/ Toward the tail or in a posterior direction.
caudal /CAWD-əl/ (1) of or pertaining to the tail; (2) in humans: inferior in position; (3) in animals: toward the tail.
caul A vernacular term for the amnion.
cauterize (British: cauterise) /CAWT-ə-rize/ To burn tissue in order to destroy or sterilize it.
cautery /CAWT-ə-ree/ A means of cauterizing tissue.
cave paintings Ancient paintings created in subterranean caverns aby prehistoric humans. MORE INFORMATION
cavity /CAV-ə-tee/ A space, whether small (as in tooth caries) or large (as in the cranial or abdominal cavities), within the body.
cc Cubic centimeter.
CD molecule Cluster of differentiation molecule.
cDNA Complementary DNA.
CDP Cytidine diphosphate.
CDR Complementarity determining region.
cell biology See: cytology.
cell line See: clone.
cell membrane See: plasma membrane.
cell sap The liquid inside a vacuole.
cellulose /SELL-yəl-ose/ Fibrous carbohydrate that acts as a structural framework of plants; indigestible by humans, but serves as a food source for many other organisms. About one-third of all plant matter is cellulose, which is the most abundant organic compound on earth. — cellulosic /SELL-yə-LAW-sick/ of, pertaining to, or containing cellulose
cell wall (1) in some eukaryotic cells, a rigid capsule enclosing the plasma membrane; in plants it contains cellulose and lignin; in fungi, chitin; (2) in prokaryotes, a stiff capsule enclosing the cell membrane.
cementum /sə-MENT-əm/ (also cement /sə-MENT/) The bony substance coating the roots of teeth.
Cenozoic Era or Caenozoic /SEEN-ə-ZŌ-ick, SEHN-/ (also Cainozoic or Kainozoic /KƎN-ə-ZŌ-ick, KANE-/) The most recent geological era, which has lasted from 65.5 mya to the present.
centimorgan (cM) /SENT-ə-MORE-gən/ See: Morgan unit.
centrifugate /sen-TRIF-yə-gət/ A product of centrifugation.
centrifugate /sen-TRIF-yə-gate/ To subject to centrifugation.
centrifugation /sen-trə-f(y)oo-GAY-shən/ Processing with a centrifuge.
centrifuge /SEN-trə-fyooj/ A machine used to separate the constituents of liquid mixtures by spinning them at high speeds.
cerebrospinal /SARE-ə-brō-SPINE-əl/ Pertaining to the brain and spinal cord.
cerebrospinal axis /SARE-ə-brō-SPINE-əl/ The central nervous system.
cerebrospinal fluid /SARE-ə-brō-SPINE-əl/ The liquid surrounding the brain and spinal cord.
cervical /SƏR-və-kəl/ Of or pertaining to the neck, or a necklike part such as the cervix uteri.
cervix uteri /SƏR-vix YOOD-ər-ee/ The outer, narrow neck of the uterus.
Cetacea /see-TAY-shə/ The mammalian order that includes whales, dolphins, and porpoises.
cetotolite /see-TOAD-ə-lite/ A fossil whale bone.
chaetognaths (common name: arrow worms) /KEED-əg-naths; KEE-dog-/ Small worms in the phylum Chaetognatha (chaeto = bristly and gnath = jaw). They range in size from 2 mm to 12 cm in length, depending on the form in question, and occupy a broad range of marine environments. Most chaetognaths are transparent. PICTURE | PICTURE | ANATOMY
chaetotactic /kee-dō-TACK-tick/ Pertaining to chaetotaxy.
chaetotaxy /kee-dō-TACKS-ee/ The study of the arrangement of bristles on arthropods.
Chalcolithic /KALK-ə-LITH-ick/ The Copper Age; the first phase of the Bronze Age, during which tools were made of pure copper (without the addition of tin to form bronze).
cheilectropion (also chilectropion) /kī-lek-TROPE-ee-awn, -ən/ Eversion of the lips.
chimera (British: chimaera) /kī-MIR-ə, kə-/ (1) an organism combining cells from two or more different genetic sources. A chimera can be produced, for example, by pushing together two genetically distinct early-stage embryos and then allowing them to develop; (2) a molecule composed of molecules of two distinct types (e.g., a DNA-RNA chimera).
chimeraplasty A process for the experimental, targeted repair of DNA.
chiragra /kī-RAWG-rə/ Pain in the hand.
chiroplasty /KĪ-rō-PLAST-ee/ Plastic surgery of the hand.
chirospasm /KĪ-ro-SPAZ-əm/ Writer's cramp, or painful, spasmodic muscle contractions in the hand.
chitin /KITE-in/ A structural polysaccharide that is the main component of the exoskeletons of all arthropods and the cell walls of fungi. It is also found in many mollusks, for example, in radulae and in the beaks of cephalopods. Chitin is a high-molecular-weight polymer made up of N-acetylglucosamine residues. STRUCTURE OF TWO LINKED RESIDUES
chitinous /KITE-in-əs/ Composed of chitin.
chlorine (Cl) /KLORE-een/ Chemical element (atomic weight 35.453, atomic number 17). A corrosive, poisonous gas. When inhaled, it destroys the mucous membranes of the respiratory passages (this effect can be countered by inhaling ammonia or alcohol fumes). Combines with sodium to form common salt (NaCl). PERIODIC TABLE
cholera /CALL-er-ə/ An acute infectious form of gastroenteritis caused by endotoxin-producing strains of the bacterium Vibrio cholerae. Contagion is through ingestion of foods and liquids contaminated with the excreta of infected individuals.
chondriome /KAWND-ree-ome/ All the mitochondria of a cell taken together.
chondrosarcoma /KAWN-drō-sar-KŌ-mə/ A sarcoma forming in bone cartilage (except "extraskeletal chondrosarcoma", which forms, not in bone cartilage, but in the soft tissues of the upper arms or legs). Chondrosarcoma is more common in people over 40.
chorea /kore-REE-ə/ A disorder characterized by involuntary, spasmodic movements of the face and extremities.
chorion /KORE-ee-awn/ The outermost of the four membranes surrounding a mammalian embryo.
chorionic gonadotropin (CG) /kore-ee-AWN-ik gə-NAD-ə-TROPE-ən/ A hormone stimulating production of progesterone. It is itself produced by the placenta and is the hormone usually assayed for by pregnancy tests.
chromonema (pl chromonemata) /KROME-ə-NEEM-ə/ The thread of DNA within chromatin.
chromosome /KROME-ə-zome/ A physically discrete portion of the genome carrying many genes. Eukaryotic chromosomes are composed of chromatin. Prokaryotic chromosomes are single, circular, and do not contain a histone scaffold (that is, they are not composed of chromatin. Eukaryotic chromosomes are multiple and linear. The name chromosome, meaning "colored body," was inspired by the fact that in early studies of cellular structure the chromosomes could be easily stained with colored dyes and therefore showed up as colored bodies under the microscope. MORE INFORMATION
chromosome number (also chromosome count) /KROME-ə-zome/ The number of chromosomes in a eukaryotic cell. Each eukaryote has a characteristic chromosome number, which is the typical number of chromosomes found in each of its cells.
chromosome painting /KROME-ə-zome/ Attachment of a fluorescent dye to particular chromosomes, or parts of a chromosome having an affinity for the dye. See: spectral karyotype.
chromosome pair (also homolog pair) /KROME-ə-zome/ A pair of homologs.
chromosome set /KROME-ə-zome/ (1) in an organism that lacks sex chromosomes: a set of chromosomes that includes one and only one of each of the different types of chromosomes characteristic of that organism; (2) in an organism having sex chromosomes: a set of chromosomes that includes one and only one of each of the different types of autosomes characteristic of that organism, plus either one of the sex chromosomes.
chronobiology /KRŌ-nə-bī-AWL-ə-jee/ The study of time-dependent phenomena in living organisms — chronobiologist /KRŌ-nə-bī-AWL-ə-jist/
chronograph /KRŌ-nə-graf/ An instrument for recording the exact time of events — chronographic /KRŌ-nə-GRAF-ick/ — chronographically /KRŌ-nə-GRAF-ick-lee/
chronospecies /KRŌ-nə-SPEE-seez/ A fossil form assigned a distinct binomial name because it occurred at a different time from other, similar forms. However, there is no generally accepted definition of the term species. MORE INFORMATION.
chrysalis /KRIS-ə-lis, -ləs/ An enclosed, immobile stage during the development of many insects that undergo metamorphosis.
chthonophagia /thawn-ō-FAY-gee-ə/ The consumption of earth or clay in the diet.
chyle /kile/ The milklike substance contained within the lacteals and the lymphatic vessels of the intestine, a solution of the digestive products, it consists primarily of fats.
chylidrosis /kile-ə-DRŌ-səs, -sis/ White sweat resembling chyle.
chylifacient /kile-ə-FAY-shənt/ Producing chyle.
chylology /kile-AWL-ə-jee/ The study of chyle.
chyme /kime/ The liquid mass of partially digested food found in the stomach and small intestine.
cilia /SILL-ee-ə/ (sing cilium /SILL-ee-əm/) (1) eyelashes; (2) tiny hairlike processes covering certain internal surfaces of the body such as the epithelial surfaces of the respiratory tract or the internal lining of the inner ear; (3) hairlike processes found on certain cells and microorganisms.
ciliary body /SILL-ee-AIR-ee/ The ring of ciliary muscles (which control the iris) together with the cilia that connect them to the iris. The ciliary body itself connects the choroid with the iris.
circulatory system (also cardiovascular system) The heart, blood vessels, and lymphatic vessels, taken together as a system. DIAGRAM
cleidocostal /klī-dō-KOST-əl/ Pertaining to both clavicle and rib.
cleidoic egg /klī-DŌ-ik/ A shelled egg permeable only to gases.
cleistocarp /KLĪ-stə-karp/ Cleistothecium.
cleistogamy /klī-STAW-gə-mee/ Self-pollination that occurs before the flower opens.
cleistothecium /KLī-stə-THEESH-ee-əm/ A closed spore-bearing structure ("fruiting body") found in fungi; the spores are released as it decays.
cline A graded series of differences exhibited within a population (usually along a geographic line or across a region of environmental transition).
cloaca The single excretory opening present in reptiles, birds, as well as in echidnas and in the platypus (cloaca means sewer in Latin); it serves as a passage for the expulsion of urine, feces, and reproductive fluids, as well as eggs.
clomiphene A chemical stimulant that causes ovaries to release eggs.
clone Two or more molecules, cells, or organisms identical to some ancestral molecule, cell, or organism. MORE ABOUT ORGANISMAL CLONES
clone bank See: genomic library.
clonic /KLONE-ik, KLAWN-/ Pertaining to clonus.
cloning (1) producing multiple, exact copies (clones) of a single segment of DNA to obtain sufficient material for further study. This process is called "cloning DNA." The resulting collections of cloned DNA molecules are referred to as "clone libraries" (see: cloning vector); (2) producing by the natural process of cell division many copies of a cell. The collection of cloned cells identical to the original cell, is called a cell line. (3) producing complete, genetically identical organisms via mitosis (read more about organismal clones). See also: cloning vector.
cloning vector A virus, plasmid, bacteriophage, chromosome, or eukaryotic cell used to carry and replicate a DNA sequence of interest so that more copies of that DNA can be produced; also can be used for producing the protein product of a particular DNA sequence.
clonus /KLONE-əs/ Involuntary, sudden, and alternating contraction and relaxation of a muscle or group of muscles.
cluster of differentiation molecules (CD molecules) Cell-surface molecules that are recognized by particular sets of monoclonal antibodies. CD molecules are used to identify cell types, and the stage of differentiation and activity of cells. As soon as two specific monoclonal antibodies (mAb) have been shown to bind to a particular CD molecule, it is assigned a number. If the molecule has not been well characterized, or has only one mAb, it is usually assigned the provisional indicator w (e.g., "CDw29"). The CD designation system was originally conceived for the classification of leukocytes, but is now used for a wide variety of cell types.
C-meiosis /SEE-mī-Ō-səs/ Colchicine-blocked meiosis.
C-metaphase /see-MED-ə-faze/ Colchicine-blocked metaphase.
C-mitosis /SEE-mī-TŌ-səs/ Colchicine-blocked mitosis; treating mitotic cells with colchicine allows easier detection and identification of chromosomes than in normal mitosis. During the long metaphase of a C-mitosis the chromosomes are still connected at the centromere, but the chromatids of each chromosome pair repel each other. The chromatids do eventually separate, but they don't segregate. Instead, a single nuclear envelope develops and encloses them all. The individual chromatids then replicate during interphase state. The result is a cell with a doubled chromosome count. For example, diploid cells treated with colchicine yield tetraploid cells.
CMP (1) cytidine monophosphate; (2) cAMP receptor protein (catabolite activator protein).
Cnidaria /nī-DAR-ee-ə/ The phylum containing jellyfishes, sea anemones, corals, and hydroids. The body of a cnidarian is made up primarily of mesoglea contained in a bag of thin epithelium. The diagnostic feature of a cnidarian is the cnidocyte, a cell that fires a toxin projectile. MORE INFORMATION
cnidocyst /NĪ-də-sist/ See: nematocyst.
cnidocyte /NĪ-də-sīght/ See: nematocyst.
CoA Coenzyme A.
CoA-SH Reduced coenzyme A.
coccus (pl cocci) /KAWK-əs, pl KAWK-ee, -eye, -see, -sigh/ Any spherical or ovoid bacterium.
coccygodynia /KAWK-sə-go-DIN-ee-yə/ Pain in the coccyx.
coccyx /KAWK-six, -səx/ The last bones of the spine, of which there are usually four (though there may be as many as six). They are usually ankylosed. The coccyx (commonly called the "tailbone") articulates with the sacrum. PICTURE
cochlea /KŌK-lee-ə/ A spiral tube, shaped like a snail shell and forming part of the inner ear. It winds around a central bony axis, the modiolus. The cochlea contains the organ of Corti, the receptor that translates sound waves into nerve impulses. PICTURE
code See: genetic code.
coding strand The strand of a duplex DNA molecule that has the same nucleotide sequence as the mRNA (except that Ts appears in the DNA where Us appear in the corresponding RNA). The coding strand is antisense strand because it does not serve as the template for mRNA synthesis.
codon /KŌ-dawn/ See: genetic code.
coefficient of variation (C or C.V.) /kō-ə-FISH-ənt/The standard deviation divided by the mean and multiplied by 100.
coenzyme /KŌ-ehn-zīm/ An organic molecule required for an enzyme's function. Most vitamins are coenzymes.
coenzyme A (CoA) /KŌ-ehn-zīme/ An important intermediate in the metabolism of fatty acids, amino acids, and pyruvate.
coenzyme Q₁₀ (also coenzyme Q, ubiquinone, ubidecarenone, CoQ₁₀ CoQ, Q10, Q) /KŌ-ehn-zīme/ A molecule present in most eukaryotic cells, especially the mitochondria. As a component of the electron transport chain, it takes part in aerobic respiration, generating energy in the form of ATP.
cofactor /KŌ-fak-ter/ Any molecule or ion required for an enzyme's function.
cognition /kawg-NISH-un/ Conscious intellectual activity.
cognitive /KAWG-nə-tive/ Pertaining to cognition.
cohort /KŌ-hort/ In a population, all individuals of given age.
Coleoptera /KŌ-lee-AHP-ter-ə/ The largest insect order, containing the beetles. The name is derived from beetles' ability to sheathe their wings (Coleo- = sheath and -ptera = wing). The sheath with which a beetle covers its folded wings is called an elytron.
coleoptile /kō-lee-AWP-təl/ The first leaf of a monocotyledon.
colloid /KŌ-loid/ A substance, such as starch, albumin, or gelatin, that shows little or no tendency to diffuse across membranes even when thoroughly mixed with a liquid. A colloid mixed with a liquid is not actually dissolved and does not cause some of the effects usually associated with a solute (e.g., increases in the freezing point, boiling point, and vapor pressure of the liquid).
colon /KŌ-lən/ See: large intestine.
commensalism /kə-MEN-sə-LIZ-əm/ A form of symbiosis in which one of the two participants benefits, but the other is not harmed.
colpocele /KOLE-pə-seel/ Vaginal hernia.
commissure /kə-MISH-er/ Line of union, the place where two bodily structures join or meet.
comparative anatomy /ə-NAT-ə-mee/ The scientific study of similarities and differences in the bodily structures (anatomies) of distinct types of animals — comparative anatomist /ə-NAT-ə-məst, -mist/
comparative genomics /jə-NOME-iks, -əks/ A method of bioinformatic analysis that characterizes genetic motifs by comparing the genomes of different model organisms.
complementary DNA (cDNA) /kom-plə-MENT-er-ee/ A DNA sequence generated from an RNA (usually mRNA) template. If the introns have been processed out of the RNA, the resulting cDNA will differ from the gene that originally produced the RNA. See also: messenger RNA.
complementary sequence /kom-plə-MENT-er-ee/ A single-stranded nucleotide sequence that can form a double-stranded structure with another single-stranded sequence. For example, the complementary sequence to CATG is GTAC — complementarity /kom-plə-men-TARE-ə-tee/ Complementary Sequence Tool
complex trait A non-Mendelian trait that does not follow the ordinary pattern of inheritance. Usually involves interaction of two or more genes or interactions between a gene and the environment. See also: additive genetic effects.
computational biology See: bioinformatics.
concentration The relative amount of solute dissolved in a given amount of solvent. The concentration of a solution may be described as dilute (containing a relatively small proportion of solute) or concentrated (containing a relatively large proportion of solute). The concentrations of solutions are expressed in various ways. One is to specify the weight of solute in a given weight of solvent (e.g., 10 g NaCl in 100 g water); a 1% solution NaCl solution by weight contains 1 g NaCl in 100 g water. Another common method is to express the concentration of a solution in terms of its molarity.
concerted evolution /kən-SERT-əd/ Evolution of a gene family in which members of the family occurring at different loci in the same type of organism remain more similar to each other than are versions occurring at the same locus in distinct types of organisms.
condyle /KAWN-dīl, -dəl/ A bulge or knob forming the bearing surface of a joint (the term is used, usually, when the joint contains a pair of such prominences; the term head is employed when only a single prominence is present).
congenic strains /kən-JEN-ik/ Nearly identical strains differing only with respect to a small chromosomal segment. Compare: coisogenic strains.
congenital trait /kən-JEHN-ə-təl/ A trait present at birth, and not produced by environmental influences.
conglomerate /kən-GLAWM-er-rət/ Coarse-grained (clasts > 2mm in diameter) sedimentary rock.
coniform /KAWN-ə-form, KONE-/ Cone-shaped.
coniology See: koniology.
conjugated /KAWN-jə-gate-əd/ Joined, attached.
conjugated protein /KAWN-jə-gate-əd/ A protein that is attached to some other non-protein chemical group.
conjunctiva /kən-jənk-TĪ-və/ Clear mucous membrane that lines the sclera and the interior of the eyelids.
connective tissue /kə-NECK-tiv, -təv/ One the four categories to which tissue has traditionally been assigned, the other three being muscle, epithelial tissue, and nervous tissue. Under this system, any tissue that does not fall into one of these last three categories (muscle, epithelial tissue, or nervous tissue) is classed as "connective."
conodont /KAWN-ə-dawnt, KOAN-/ An extinct, eel-like animal, long known only from its coniform teeth. Conodonts died out about 200 million years ago. PICTURE
conotoxins /kō-no-TAWKS-əns/ Toxins produced by snails of the genus Conus.
conservation biology /buy-AWL-ə-jee/ The branch of biology concerned with habitat preservation, the prevention of extinction, and conservation of biodiversity — conservation biologist /buy-AWL-ə-jəst, -jist/
constitutive /kən-STITCH-ə-tiv/ Occurring on an ongoing basis, without regard to physiological demand.
constitutively /kən-STITCH-ə-tiv-lee/ Ongoingly, without regard to physiological demand.
contagious /kən-TAY-jəs/ Capable of spreading from an infected individual to another, uninfected individual.
contig /KAWN-tig/ A nucleotide sequence constructed by assembling overlapping cloned nucleotide sequences. A contig represents a region of some particular chromosome.
contig map /KAWN-tig/ A genetic map depicting the relative order of the overlapping clones lying within a contig.
contraceptive /KAWN-trə-SEHP-tiv/ (1) preventing conception or pregnancy; (2) n. an agent preventing conception or pregnancy — contraception /KAWN-trə-SEHP-shən/
COPD Chronic obstructive pulmonary disease.
copal /KŌ-pəl, kō-PALL/ A resin produced by tropical trees; many fossil insects have been found in copal. The preservation can be exquisite, with many of these ancient insects retaining every detail and color — even of the wings and eyes. PICTURE OF 100,000-YEAR-OLD INSECTS IN COPAL
copper (Cu) /KAWP-er/ ABOUT COPPER >>
coprolites /KAWP-rə-lites/ Pieces of fossilized excrement. Coprolites can be analyzed to determine the diets of extinct organisms.
coprophilic /KAWP-rə-FILL-ik/ Attracted to excrement.
coprozoic /KAWP-rə-ZŌ-ik/ Living in excrement.
CoQ or CoQ₁₀ Coenzyme Q₁₀.
cord An anatomical structure resembling an ordinary cord, as a spinal cord.
cordiform /KORD-ə-form/ Heart-shaped.
corectomy /kore-ECK-tə-mee/ Surgical excision of the iris.
corm /KAWRM, KAWM/ A short, swollen underground stem present in certain plants. Corms differ from bulbs in that they lack interior layering and in having a structure like that of a stem.
cormoid /KAWRM-oid/ adj. Cormlike.
cormose /KAWRM-ose/ or cormous /KAWRM-əs/ adj. Having corms.
cornea /KORN-ee-yə/ The transparent external layer of the eye that overlies the iris. PICTURE
coronary /KORE-ə-NARE-ee/ Of or relating to the heart.
correlation /kor-ə-LAY-shən/ The degree to which two statistical variables vary together; usually measured in terms of the correlation coefficient. When there is a positive correlation between two variables an increase in one is associated with an increase in the other; with a negative correlation an increase in one variable is associated with a decrease in the other.
correlation coefficient (r) /kor-ə-LAY-shən/ A common measure of correlation, r = cov(x,y)/sxsy, where cov(x,y) is the covariance between samples x and y, sx is the standard deviation of sample x, and sy is the standard deviation of sample y. Note that 1 ≥ r ≥ -1, and that r = 1 indicates a perfect positive correlation, r = -1 indicates a perfect negative correlation, and r = 0 indicates a lack of correlation.
cotyledon /KAWT-ə-LEE-dən/ An embryonic seed leaf. The cotyledons function in absorbing nutrients from the seed before the embryo is sufficiently developed to be capable of photosynthesis. Angiosperms are classified as one of two major types, either monocotyledons or dicotyledons, on the basis of the number of cotyledons present in the embryo.
covalent bond /kō-VALE-unht/ A strong chemical bond where two atoms share a single pair of electrons.
covariance (cov) /kō-VARE-ee-əns, KŌ-vare-ee-əns/ The covariance is used to calculate the correlation coefficient. For samples of size N, the covariance between samples x and y is defined by the formula cov(x,y) = [(x₁ - xbar)(y₁ - ybar) + (x₂ - xbar)(y₂ - ybar) +, ..., + (xN - xbar)(yN - ybar)]/N, where xbar is the mean of sample x, and ybar is the mean of sample y.
Cowper's glands A pair of pea-sized glands on either side of the prostate that secrete fluids into the urethra.
coxa/CAWCK-sə/ (pl coxae /CAWCK-sigh/) (1) the hip; (2) the hip joint.
coydog (also dogote) /COY-dawg; daw-GŌ-dee/ A hybrid produced by mating between a domestic dog (Canis familiaris) and a coyote (Canis latrans).
cpm Counts per minute (of radioactivity).
cranial /KRAYN-ee-əl/ Of, or relating to, the cranium.
cranial capacity /KRAY-nee-əl/ The volume of an individual's braincase (usually measured in cubic centimeters).
cranium /KRAY-nee-əm/ The portion of the skull enclosing the brain.
crescentic /krə-SENT-ick/ Crescent-shaped.
craton /KRAY-tawn, KRAT-tawn/ A (continental) portion of the Earth's curst that is stable and that has not undergone deformation for a long period of time; adj.: cratonic /krə-TAWN-ik, kray-, krat-/.
Cretaceous Period (K) /krə-TAY-shəs/ A geologic period that lasted from approximately 145.5 to 65.5 mya. It was a period of warm climates and high sea levels. Its name derives from the Latin word for chalk (creta) since some of the earliest Cretaceous formations studied were composed of that substance. GEOLOGIC TIME SCALE
Cretaceous-Tertiary (KT) mass extinction /krə-TAY-shəs TARE-shee-air-ee, -share-ee/ The mass extinction that occurred at the end of the Cretaceous Period (and of the Mesozoic Era). It is generally believed that the dinosaurs became extent at this time (this issue is discussed at length elsewhere on this website).
Cretaceous Western Interior Seaway /krə-TAY-shəs/ A sea that divided the eastern and western portions of North America 130 to 70 million years ago. MORE INFORMATION
crocodilians /krock-ə-DILL-ee-əns/ Alligators, crocodiles, and gharials.
Cro-Magnon /krō-MAG-nən/ Name long used to refer to the first modern humans (Homo sapiens) to reside in Europe; The name is derived from Cro-Magnon Cave in southwest France, where ancient individuals of the modern type were discovered in the nineteenth century. In scholarly literature this name has now fallen into disuse. MORE INFORMATION
cross (1) n. a mating between two distinct types of organisms; (2) n. an offspring produced from such a mating; a hybrid; (3) v. to mate, or cause to mate, with an individual of some distinct type. MORE INFORMATION
crossability n. the degree to which two distinct types of organisms can be successfully crossed.
crust /krəst/ The outermost layer of the Earth. The crust is thinnest — about 6 miles (~10 km) thick beneath the oceans — and thickest — about 40 miles (~65 km) beneath the the continents. The crust makes up less than 1 % of the Earth's volume.
crustacean /krəs-TAY-shən/ An animal belonging to the major arthropod group Crustacea, which includes such animals as crabs, shrimp, and lobsters.
cryobiology /crī-ō-bī-AWL-ə-jee/ The study of the effects of low temperatures on living organisms — cryobiologist /crī-ō-bī-AWL-ə-jist/
cryophile /CRĪ-ə-file/ A cold-loving organism.
cryptobiology /krip-tō-bī-AWL-ə-jee/ The investigation of the possible of existence of concealed organisms, or of ones living in inaccessible environments where they might easily go undetected — cryptobiologist /krip-tō-bī-AWL-ə-jist/
cryptorchid /kript-ORE-kid/ An individual with testicles that have not descended into the scrotum — cryptorchidism /krip-TORE-kid-iz-əm/
C-terminal (or C-terminus) Carboxyl terminal
Culex /KYOO-leks/ A genus of mosquitoes serving as vectors for such diseases as filariasis, St. Louis encephalitis, West Nile virus, Japanese encephalitis, and avian malaria. ADULT ANATOMY | LARVAL ANATOMY | LIFE CYCLE
cuneate /KYOO-ee-ate, -ət/ Wedge-shaped.
cuneiform /kyoo-NAY-ə-form/ Wedge-shaped.
cusp /kəsp/ A point on the occlusal surface of a tooth; (2) one of the flaps of a cardiac valve; (3) in botany, any rigid pointed structure.
cutaneous /kyoo-TANE-ee-əs/ Of or pertaining to skin.
cuticle /KYOOT-ə-kəl/ (1) outermost layer or investment of an organism, particularly the exoskeleton an arthropod; usually made up of fibrous materials such as collagen or chitin, and in some cases strengthened by the addition of minerals (e.g., calcium carbonate) (2) a waxy external layer, that prevents drying; found on the outer surface of many plants.
cutis /KYOO-təs/ The skin.
cyanobacteria /sī-AN-ō-bac-TEER-ee-ə/ Photosynthetic prokaryotes, known from the earliest stages of the fossil record.
cyanosis /sī-ə-NŌ-səs/ Bluish skin coloration due to high levels of reduced hemoglobin in the blood.
cyclitis /sə-KLIDE-əs, sī-/ Inflammation of the ciliary body.
cyclopia /sī-KLOPE-ee-ə/ A rare developmental anomaly in which only a single, usually medial, eye is present.
cyclostomate /sick-KLOSS-tə-mət/ (1) possessing a circular mouth; (2) belonging to the Cyclostomata.
cynocephalus or kynocephalus /KĪ-nō-SEF-ə-ləs/ A abnormal human fetus having a head like that of a dog. MORE INFORMATION
cystitis /sis-TĪT-əs/ Inflammation of the bladder.
cytidine /SĪT-ə-deen/ Cytosine attached to a ribose ring.
cytidine triphosphate /SIGHT-ə-deen/ Cytidine with an added triphosphate; in metabolic processes cytidine triphosphate is used as a source of energy in the same way as ATP, but its role is more specific than that of ATP, because it does not participate in as wide a variety of processes.
cytogenesis /SĪT-ə-JEN-ə-səs/ The origin and development of a cell.
cytogenetics /SĪT-ə-jə-NET-iks/ The study of the physical appearance of chromosomes. See also: karyotype.
cytology (also cell biology) /sī-TALL-ə-jee/ The study of living cells, in particular, their physiological properties, life histories, structures, organelles, and method of division — cytologist /sī-TALL-ə-jist/
cytolysis /sī-TAWL-lə-səs/ Cell lysis.
cytolytic /sī-tə-LIT-ick/ Causing cytolysis.
cytometer /sī-TOM-ə-tur/ An instrument for counting the number of cells in a sample.
cytoplasmic inheritance /sī-tō-PLAZ-mick/ See: cytoplasmic trait.
cytoplasmic trait /sī-tō-PLAZ-mick/ A trait governed by genes found outside the nucleus in mitochondria or chloroplasts. Such traits are inherited only from the mother. Such inheritance is known as cytoplasmic, or uniparental, inheritance.
cytoskeleton /SĪ-tə-SKEHL-ə-tən/ A fibrous network of microtubules and microfibers in eukaryotic cells that gives shape to the cell, anchors organelles, serves a variety of transport functions within the cell, and, in some cases, allows the cell to move or change shape.
cytosol /SĪ-tə-sawl/ The fluid portion of cytoplasm.
cyturia /sī-TER-ee-yə/ Presence of cells (of any type) in the urine.
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