| random mating equilibrium | <genetics> In a population containing the genotypes of AA, aa, and Aa, the frequency of AA will be p2, the frequency of aa will be q2, and the frequency of Aa will be 2 pq at equilibrium, where p is the frequency of A and q is the frequency of a. By the Hardy-Weinberg law, a ramdonly-mating population will eventually reach these frequencies and be at this equilibrium as long as there are no selection pressures on the population. (09 Oct 1997) |
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| genetic equilibrium | A condition in which the rate of an allele's forward mutation is cancelled out by its rate of reverse mutation. (09 Oct 1997) |
| Gibbs-Donnan equilibrium | An equilibrium established between a charged, immobile colloid (such as clay, ion exchange resin or cytoplasm) and a solution of electrolyte. Characteristics: ions of like charge to the colloid tend to be excluded, ions of opposite charge tend to be attracted, the colloid compartment is electrically polarized relative to the solution in the same direction as the colloid charges (a Donnan potential) and the osmotic pressure is higher in the colloid compartment. (18 Nov 1997) |
| chemical equilibrium | <chemistry> A state in a reversible chemical reaction at which the reactants are turning into products at the same rate as the products are turning back into the reactants, so that the amounts of each reactant and product remains constant. (09 Oct 1997) |
| physiologic equilibrium | nutritive equilibrium |
| Hardy-Weinberg equilibrium | <genetics> In a population containing the genotypes of AA, aa, and Aa, the frequency of AA will be p2, the frequency of aa will be q2, and the frequency of Aa will be 2 pq at equilibrium, where p is the frequency of A and q is the frequency of a. By the Hardy-Weinberg law, a ramdonly-mating population will eventually reach these frequencies and be at this equilibrium as long as there are no selection pressures on the population. (09 Oct 1997) |
| secular equilibrium | A type of radioactive equilibrium in which the half-life of the precursor (parent) radioisotope is so much longer than that of the product (daughter) that the radioactivity of the daughter becomes equal to that of the parent with time. Stable equilibrium, equilibrium in which, after every small perturbation, the original state will tend to be restored. Transient equilibrium, a type of radioactive equilibrium in which the half-life of the parent radioisotope is longer than that of the daughter so that the ratio of activities of parent and daughter become constant as they decrease with time. Unstable equilibrium, equilibrium in which the response to a small perturbation will tend to make the perturbation greater (e.g., a logged feedback process of zero order). (05 Mar 2000) |
| homeostatic equilibrium | See: homeostasis. Nitrogenous equilibrium, a condition in which the amount of nitrogen excreted from the body equals that taken in with the food; nutritive equilibrium so far as protein is concerned. Nutritive equilibrium, condition in which there is a perfect balance between intake and excretion of nutritive material, so that there is no increase or loss in weight. Synonym: physiologic equilibrium. (05 Mar 2000) |
| sense of equilibrium | The sense that makes possible a normal physiologic posture. Synonym: static sense. (05 Mar 2000) |
| Donnan equilibrium | An equilibrium established between a charged, immobile colloid (such as clay, ion exchange resin or cytoplasm) and a solution of electrolyte. Characteristics: ions of like charge to the colloid tend to be excluded, ions of opposite charge tend to be attracted, the colloid compartment is electrically polarized relative to the solution in the same direction as the colloid charges (a Donnan potential) and the osmotic pressure is higher in the colloid compartment. (18 Nov 1997) |
| dynamic equilibrium | Balance A condition in which no further net change is occuring in a system, and free energy is minimimal. (09 Oct 1997) |
| thermodynamic equilibrium | <radiobiology> There is a very general result from statistical mechanics which states that, if a system is in thermodynamic equilibrium with another (or several other) system, all processes by which the systems can exchange energy must be exactly balanced by their reverse processes, so that there is no net exchange of energy. For plasma systems in thermodynamic equilibrium, ionisation must be balanced by recombination, Bremsstrahlung by absorption, and so on. When thermodynamic equilibrium exists, the distribution function of particle energies and excited energy levels of the atoms can be obtained from the Maxwell-Boltzmann distribution (which is a function only of the temperature). The Saha equation is a special application of this. (09 Oct 1997) |
| equilibrium | Balance A condition in which no further net change is occuring in a system, and free energy is minimimal. (09 Oct 1997) |
| equilibrium centrifugation | A type of density gradient centrifugation used to separate proteins or nucleic acids from a mixture. (09 Oct 1997) |
| equilibrium constant | <chemistry> The ratio of the reverse and forward rate constants for a reaction of the type: A + B = AB at equilibrium the equilibrium constant (K) equals the product of the concentrations of reactants divided by the concentration of product and has dimensions of concentration. Kd = (concentration A.concentration B) / (concentration AB). The affinity constant (Ka) is the reciprocal of the equilibrium constant. Dimension: moles per litre. In general the concept of Kd is more readily understood than that of Ka, for example: in considering the conversion of A to AB by the binding of ligand B, the Kd = B when A = AB. Thus Kd is equal to the ligand concentration which produces half maximal conversion (response). (10 Jan 1998) |