Variability is one of the main properties of a living organism to acquire new features and properties. A distinction is made between genotypic (hereditary), caused by changes in the genotype of one individual or a small number of individuals in a population, i.e. mutations, and modification (non-hereditary), when changes occur gradually under the influence of external environmental factors in all individuals of the population.
The ability of living organisms to acquire new traits and qualities. It is expressed in an infinite variety of traits and properties in individuals of different degrees of relatedness. When classifying the types and forms of variability, certain aspects of this universal property are emphasized. Taking into account the causes and nature of changes, two main types of variability are usually distinguished.
Hereditary, or genotypic, variability is caused by changes in the genetic material (genotype) that are transmitted from generation to generation. Changes in the genotype can be caused by mutations - changes in the structure of genes and chromosomes or changes in the number of chromosomes in the chromosome set. In mutational variability, new variants (alleles) of genes arise, and mutations are relatively rare and sudden. Another form of genotypic variability is combinative variability, which is based on recombination (rearrangement) of chromosomes and their sections during sexual reproduction (during meiosis and fertilization). As a result, the set of genes and, consequently, traits in the offspring always differs from the set of genes and traits in the parents. Combinative variability creates new combinations of genes and provides both the entire diversity of organisms and the unique genetic individuality of each of them.
Non-heritable, or modification variability is the ability of organisms to change under the influence of various environmental factors (temperature, humidity, etc.). This type of variability is not associated with changes in the genotype and is not inherited. However, the limits of modification variability of any trait are set by the genotype. The degree of variation of a trait, i.e., the breadth of the reaction norm, depends on the importance of the trait: the more important the trait, the narrower the reaction norm. Modification variability has a group character - changes (modifications) occur in all individuals of a population that is exposed to a certain external influence. Another feature is reversibility: modifications usually disappear immediately or gradually when the factor that caused them is eliminated.