| G+C ratio | <molecular biology> In DNA (or RNA) from any organism, the percent of the total nucleic acid that consists of guanine plus cytosine bases. (20 Mar 1998) |
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| ratio | 1. <mathematics> The relation which one quantity or magnitude has to another of the same kind. It is expressed by the quotient of the division of the first by the second; thus, the ratio of 3 to 6 is expressed by 3/6/ or 1/2; of a to b by a/b; or (less commonly) the second is made the dividend; as, a:b = b/a. Some writers consider ratio as the quotient itself, making ratio equivalent to a number. The term ratio is also sometimes applied to the difference of two quantities as well as to their quotient, in which case the former is called arithmetical ratio, the latter, geometrical ratio. The name ratio is sometimes given to the rule of three in arithmetic. See Rule. 2. Hence, fixed relation of number, quantity, or degree; rate; proportion; as, the ratio of representation in Congress. Compound ratio, Duplicate ratio, Inverse ratio, etc. See Compound, Duplicate, etc. Ratio of a geometrical progression, the constant quantity by which each term is multiplied to produce the succeeding one. Origin: L, fr. Reri, ratus, to reckon, believe, think, judge. See Reason. Source: Websters Dictionary (01 Mar 1998) |
| ratio imaging fluorescence microscopy | <procedure> A method of measurement of intracellular pH or intracellular calcium levels, using a fluorescent probe molecule (see fura-2), in which the two different excitation wavelengths are used and the emitted light levels compared. If emission at one wavelength is sensitive to the intracellular ion level and emission at the other wavelength is not, then standardisation for intracellular probe concentration, efficiency of light collection, inactivation of probe and thickness of cytoplasm can all be performed automatically. (17 Dec 1997) |
| ratio of decayed and filled surfaces | An index of decayed and filled permanent surfaces per person, per full complement of 122 tooth surfaces. (05 Mar 2000) |
| ratio of decayed and filled teeth | An index of decayed and filled permanent teeth per person, per full complement of 28 teeth. (05 Mar 2000) |
| ratio scale | A scale that involves physical units and demonstrates their relations. (05 Mar 2000) |
| ventilation-perfusion ratio | The ratio of alveolar ventilation to simultaneous alveolar capillary blood flow in any part of the lung. (12 Dec 1998) |
| ventilation/perfusion ratio | The ratio of alveolar ventilation to simultaneous alveolar capillary blood flow in any part of the lung; because both ventilation and perfusion are expressed per unit volume of tissue and per unit time, which cancel, the units become liters of gas per liter of blood. (05 Mar 2000) |
| mass-action ratio | The ratio of the product of all of the product concentrations divided by the product of all of the reactant concentrations of a particular reaction; when the reaction has been completed (i.e., t = ∞), then this ratio is equal to the equilibrium constant. (05 Mar 2000) |
| case fatality ratio | The mortality rate of a disease, usually expressed per 100 cases. (05 Mar 2000) |
| CD4:CD8 ratio | The ratio of CD4 to CD8 cells. A common measure of immune system status that is around two in healthy individuals. The ratio of T-lymphocytes that express the CD4 antigen to those that express the CD8 antigen. This value is commonly assessed in the diagnosis and staging of diseases affecting the immune system including HIV infection. (12 Dec 1998) |
| reproductive ratio | <epidemiology> 1. Basic reproductive ratio , Ro , a dimensionless parameter which encapsulates the biological details of different transmission mechanisms. For microparasites, Ro , is defined as the average number of secondary cases of infection to which one primary case gives rise throughout its infectious period if introduced into a defined population consisting solely of susceptible individuals. For macroparasites, Ro , is the average number of female offspring (or just offspring in the case of hermaphroditic species) produced throughout the lifetime of a mature female parasite, which themselves achieve reproductive maturity in the absence of density-dependent constraints on the parasite establishment, survival or reproduction. Also known as the basic reproduction rate, number. 2. Effective reproductive ratio , R , The number of secondary cases (microparasites) or female offspring (macroparasites) produced in a host population not consisting entirely of susceptible individuals (microparasites) or within which density dependent constraints limit parasite population growth (macroparasites). Under conditions of stable endemic infection, R=1. (05 Dec 1998) |
| respiratory exchange ratio | The ratio of the net output of carbon dioxide to the simultaneous net uptake of oxygen at a given site, both expressed as moles or STPD volumes per unit time; in the steady state, respiratory exchange ratio is equal to the respiratory quotient of metabolic processes. (05 Mar 2000) |
| mendelian ratio | The ratio of progeny with a particular phenotypes or genotypes expected in accordance with Mendel's law among the offspring of matings specified as to genotype or phenotype. (05 Mar 2000) |
| M:E ratio | The ratio of myeloid to erythroid precursors in bone marrow; normally it varies from 2:1 to 4:1; an increased ratio is found in infections, chronic myelogenous leukaemia, or erythroid hypoplasia; a decreased ratio may mean a depression of leukopoiesis or normoblastic hyperplasia depending on the overall cellularity of the bone marrow. (05 Mar 2000) |