One of the most important properties of living organisms is the ability to change signs depending on environmental conditions.
Variability is the emergence of individual differences between individuals of the same species.
Due to variability, populations become genetically heterogeneous, and the species has a better chance of adapting to changing external conditions.
There are two types of variability:
- non-hereditary (phenotypic);
- hereditary (genotypic).
Non-hereditary (phenotypic) variability is the ability of a living organism (phenotype) to adapt to environmental factors within its genotype.
Phenotypic variability contributes to the adaptation of organisms to changes in environmental conditions. Thus, in domestic animals, with improved conditions, productivity increases: milk yield and fat content, egg production, etc. Hares change their coat color in winter and summer, and dandelion plants grown on poor and fertile soil differ in size, number of leaves and inflorescences.
Examples of phenotypic variability can be observed in everyday life: the human skin becomes dark under the influence of ultraviolet rays; as a result of physical exertion, muscles develop.
Hereditary (genotypic) variability is the ability of a living organism to change its genotype.
Due to genotypic variability, an individual can acquire traits that were not previously characteristic of its species. According to Darwin, genotypic variation is the main driver of evolution.
There are the following types of hereditary variability:
Mutational variability – random jump-like heritable changes in traits.
An example of mutational heredity is the appearance of albino animals, plants with altered leaf shape or unusual color of petals. So, sometimes there are dandelion plants with white or orange flowers in the inflorescence.
In humans, mutational variability is caused by phenylketonuria, polydactyly (six-fingered), Down’s syndrome, etc.
Combinative variability is the appearance in individuals of differences due to a new combination of parental genes.
It occurs during sexual reproduction. At the same time, the traits of the parental individuals are randomly combined in a number of generations, increasing the diversity of organisms in the population.
As a result of the action of various forms of variability, each natural population is characterized by a high degree of genetic heterogeneity and, due to this, is able to adapt to a constantly changing habitat.