variationArticle Free Pass variation, 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 con