| variable antigen | <immunology> Term usually applied to the surface antigens of those parasitic or pathogenic organisms that can alter their antigenic character to evade host immune responses. (See antigenic variation). (18 Nov 1997) |
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| variable deceleration | Transient foetal bradycardia usually denoting compression of the umbilical cord which may occur at any time in relation to a uterine contraction. (05 Mar 2000) |
| variable gene | <molecular biology> Those regions in the amino acid sequence of both the heavy and the light chains of immunoglobulins where there is considerable sequence variability from one immunoglobulin to other of the same class, in contrast to constant sequence (C) regions. The V regions are associated with the antigen binding areas. They contain hypervariable regions of particularly high sequence diversity. (18 Nov 1997) |
| variable region | <molecular biology> Those regions in the amino acid sequence of both the heavy and the light chains of immunoglobulins where there is considerable sequence variability from one immunoglobulin to other of the same class, in contrast to constant sequence (C) regions. The V regions are associated with the antigen binding areas. They contain hypervariable regions of particularly high sequence diversity. (18 Nov 1997) |
| variable surface glycoprotein | <protein> One of a battery of antigenicdeterminants expressed by a microorganism to elude immune detection. (09 Oct 1997) |
| random variable | A variable that may assume a set of values, each with fixed probabilities or probability densities (its distribution), in such a way that the total probability assigned to the distribution is unity; the random variable may be discrete, continuous, or mixed discrete-continuous. (05 Mar 2000) |
| mixed discrete-continuous random variable | <statistics> A random variable that may assume some values with probabilities and others with probability densities. For example, in a 35-year-old man with familial polyposis of the colon, the distribution of time until malignant disease occurs consists of a probability that he already has cancer (which would be assigned the waiting time 0), a probability density of developing it in the future and a probability that he will die of some other cause before he develops cancer. (05 Mar 2000) |
| moderator variable | A variable that interacts by virtue of being antecedent or intermediate in the causal pathway. (05 Mar 2000) |
| common variable immunodeficiency | Heterogeneous group of immunodeficiency syndromes characterised by hypogammaglobulinaemia of most isotypes, variable B-cell defects, and the presence of recurrent bacterial infections. (12 Dec 1998) |
| condenser, variable-focus | <microscopy> Essentially an Abbe condenser in which the upper lens element is fixed and the lower movable. The lower lens may be used to focus the illumination between the elements so that it emerges from the stationary lens as a large diameter parallel bundle. The field of low-power objectives may thus be filled without removing the top element. at the opposite extreme it can be adjusted to have a numerical aperture as high as 1.3. See: illumination, critical. (05 Aug 1998) |
| continuous random variable | Continuous variable that may randomly assume any value in its domain but any particular value has no probability of occurring, only a probability density. (05 Mar 2000) |
| continuous variable | A variable that may take on any value in an interval or intervals (its domain). (05 Mar 2000) |
| dependent variable | In experiments, a variable that is influenced by or dependent upon changes in the independent variable; e.g., the amount of a written passage retained (dependent variable) as a function of the different numbers of minutes (independent variable) allowed to study the passage. (05 Mar 2000) |
| discrete random variable | A random variable that may assume a countable number of values, each with a probability strictly greater than zero. (05 Mar 2000) |
| discrete variable | A variable that may assume only a countable (usually finite) number of values. (05 Mar 2000) |