| variation | In genetics, deviation in characters in an individual from those typical of the group to which it belongs, also, deviation in characters of the offspring from those of its parents. (18 Nov 1997) |
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| variation (genetics) | The phenotypic differences among individuals in a population. (12 Dec 1998) |
| antigenic variation | The phenomenon of changes in surface antigens in parasitic populations of Trypanosoma and Plasmodium (and some other parasitic protozoa) in order to escape immunological defense mechanisms. at least 100 different surface proteins have been found to appear and disappear during antigenic variation in a clone of trypanosomes. Each antigen is encoded in a separate gene. Antigenic variation is also known to occur in free living Protozoa and certain bacteria. (18 Nov 1997) |
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| phase variation | <microbiology> Alteration in the expression of surface antigens by bacteria. For example: Salmonella can express either of two forms of flagellin, H1 and H2, that are coded by different genes. Control of which form is expressed is brought about by inversion of the promoter for the H2 gene, which if functional (noninverted) is associated with the expression of H2 and the production of a repressor of the H1 gene. Inversion occurs about every 1000 bacterial divisions and is under the control of another gene, hin, that is within the invertable sequence. (31 Dec 1997) |
| coefficient of variation | The ratio of the standard deviation to the mean. (05 Mar 2000) |
| contingent negative variation | An increasing negative shift of the cortical electrical potentials associated with an anticipated response to an expected stimulus. It is an electrical event indicative of a state of readiness or expectancy. (12 Dec 1998) |
| somaclonal variation | The variation between individuals in a clone, particularly in plant clones. While the objective is usually to grow clones without variation, somaclonal variation does provide the opportunity to generate new plant types that would be harder or impossible to generate by conventional plant breeding. (14 Nov 1997) |
| isotypic variation | <immunology> Variability of antigens common to all members of a species, for example the five classes of immunoglobulins found in humans. See: idiotype and allotype. (18 Nov 1997) |
| observer variation | The failure by the observer to measure or identify a phenomenon accurately, which results in an error. Sources for this may be due to the observer's missing an abnormality, or to faulty technique resulting in incorrect test measurement, or to misinterpretation of the data. Two varieties are inter-observer variation (the amount observers vary from one another when reporting on the same material) and intra-observer variation (the amount one observer varies between observations when reporting more than once on the same material). (12 Dec 1998) |