Phenotypic (non-hereditary) variability arises under the influence of environmental factors and does not affect the genotype.
The following types of phenotypic variability are distinguished: modifications, morphoses, and phenocopies.
Modifications are non-hereditary changes in the genotype that occur under the influence of environmental factors, are adaptive in nature and are most often reversible.
Morphoses are non-hereditary changes in the phenotype that occur under the influence of extreme environmental factors, are not adaptive and irreversible (burns, scars).
Phenocopy is a non-hereditary change in the genotype that resembles a mutation (enlargement of the thyroid gland with a lack of iodine). Reversible.
- does not affect the genotype;
- in similar conditions, it manifests itself in a group of individuals;
- not inherited;
- often reversible, that is, when conditions change, the feature is not preserved.
Signs vary to varying degrees under the influence of external conditions. The limits of modification variability are determined by the norm of the reaction of the trait, which is controlled by the genotype. The reaction rate can be wide or narrow.
in chickens, body weight and egg production, depending on the conditions of detention, can vary significantly (wide reaction rate). The color of the plumage and the shape of the ridge are practically independent of the conditions (narrow reaction rate).
In butterflies of the same species, large differences in wing sizes can be observed, but the color of the wings changes little.
More often, modification variability affects quantitative traits (size, body weight, etc.) and, less often, qualitative ones.
The statistical patterns of modification variability can be expressed by the variation series and variation curve.
A variation series is a series of characteristic values arranged in ascending or descending order.
The variation curve is a graphical display of the dependence of the frequency of manifestation of a variant on its intensity.
Modification variability ensures the adaptation of the organism to changing environmental conditions within the limits of the trait reaction rate.