variation

—variational, variative /vair"ee ay'tiv/, adj. —variationally, variatively, adv.

/vair'ee ay"sheuhn/, n.

1. the act, process, or accident of varying in condition, character, or degree: Prices are subject to variation.

2. an instance of this: There is a variation in the quality of fabrics in this shipment.

3. amount, rate, extent, or degree of change: a temperature variation of 40° in a particular climate.

4. a different form of something; variant.

5. Music.

a. the transformation of a melody or theme with changes or elaborations in harmony, rhythm, and melody.

b. a varied form of a melody or theme, esp. one of a series of such forms developing the capacities of the subject.

6. Ballet. a solo dance, esp. one forming a section of a pas de deux.

7. Astron. any deviation from the mean orbit of a heavenly body, esp. of a planetary or satellite orbit.

8. Also called magnetic declination, magnetic variation. Navig. the angle between the geographic and the magnetic meridian at a given point, expressed in plus degrees east or minus degrees west of true north. Cf. deviation (def. 4).

9. Biol. a difference or deviation in structure or character from others of the same species or group.

[1350-1400; < L variation- (s. of variatio), equiv. to variat(us) (see VARIATE) + -ion- -ION; r. ME variacioun < AF < L, as above]

Syn. 1. mutation, alteration, modification; deviation, divergence, difference.

* * *

I

In biology, any difference between cells, individual organisms, or groups of organisms within a species caused either by genetic differences (variation in genotype) or by the effect of environmental factors on the expression of genetic potentials (variation in phenotype).

Variation may be shown in physical appearance, metabolism, fertility, mode of reproduction, behaviour, learning and mental ability, and other obvious or measurable characters. Genotypic variations are caused by differences in number or structure of chromosomes or by differences in the genes carried by the chromosomes. Eye colour, body form, and disease resistance are genotypic variations. Phenotypic variations may result from factors such as climate, food supply, and actions of other organisms. Phenotypic variations also include stages in an organism's life cycle and seasonal variations in an individual. Because they do not involve hereditary alteration and in general are not transmitted to future generations, phenotypic variations are not important in evolution. See also polymorphism.

II

In music, basic technique consisting of changing the music melodically, harmonically, or contrapuntally.

The simplest variation type is the variation set, in which two or more sections are based on the same musical material, which is treated with different variational techniques in each section. The practice, originally involving use of a repeated bass line (basso ostinato, or ground bass), began in early 16th-century dance music in Italy and Spain. Ground-bass forms include the chaconne and passacaglia, both of which usually employ a brief bass line repeated many times. In the 17th century, organ and harpsichord variations became a standard form in Germany. Keyboard variations in the 19th century often employed popular tunes or opera melodies; variation form was also commonly used in symphonies, quartets, and sonatas. It declined in importance after the classical era but has never ceased to be employed by composers. The music of certain non-Western cultures also uses variational techniques. The art music of southern India is built on the concept of a string of pieces, each a variation on a given "theme." A somewhat different concept of multilevel variation is found in the gamelan (orchestra) music of Indonesia. The variations are not consecutive but are simultaneous, a technique called heterophony.

* * *

▪ biology

      in biology, any difference between cells, individual organisms, or groups of organisms of any species caused either by genetic differences (genotypic variation) or by the effect of environmental factors on the expression of the genetic potentials (phenotypic variation). Variation may be shown in physical appearance, metabolism, fertility, mode of reproduction, behaviour, learning and mental ability, and other obvious or measurable characters.

      Genotypic variations are caused by differences in number or structure of chromosomes or by differences in the genes carried by the chromosomes. Eye colour, body form, and disease resistance are genotypic variations. Individuals with multiple sets of chromosomes are called polyploid; many common plants have two or more times the normal number of chromosomes, and new species may arise by this type of variation. A variation cannot be identified as genotypic by observation of the organism; breeding experiments must be performed under controlled environmental conditions to determine whether or not the alteration is inheritable.

      Environmentally caused variations may result from one factor or the combined effects of several factors, such as climate, food supply, and actions of other organisms. Phenotypic variations also include stages in an organism's life cycle and seasonal variations in an individual. These variations do not involve any hereditary alteration and in general are not transmitted to future generations; consequently, they are not significant in the process of evolution.

      Variations are classified either as continuous, or quantitative (smoothly grading between two extremes, with the majority of individuals at the centre, as height in human populations); or as discontinuous, or qualitative (composed of well-defined classes, as blood groups in man). A discontinuous variation with several classes, none of which is very small, is known as a polymorphic variation (polymorphism). The separation of most higher organisms into males and females and the occurrence of several forms of a butterfly of the same species, each coloured to blend with a different vegetation, are examples of polymorphic variation.

* * *