Variability in biology is the occurrence of individual differences between individuals of the same species. Due to variability, the population becomes heterogeneous, and the species has more chances to adapt to changing environmental conditions.
In science like biology, heredity and variability go hand in hand. There are two types of variability:
- Non-hereditary (modification, phenotypic).
- Hereditary (mutational, genotypic).
Inherited Volatility
Modification variability in biology is the ability of a single living organism (phenotype) to adapt to environmental factors within its genotype. Due to this property, individuals adapt to climate changes and other living conditions. Phenotypic variability underlies the adaptive processes that occur in any organism. Thus, in outbred animals, when conditions are improved, productivity increases: milk yield, egg production, etc. And animals brought into the mountainous regions grow undersized and with well-developed undercoat. Changes in environmental factors and cause variability. Examples of this process can be easily found in everyday life: human skin becomes dark under the influence of ultraviolet rays, muscles develop as a result of physical exertion, plants grown in shaded places and in the light have different leaf shapes, and hares change their coat color in winter and summer.
The following properties are characteristic of non-hereditary variability:
- group nature of changes;
- not inherited by offspring;
- trait change within the genotype;
- the ratio of the degree of change with the intensity of the external factor.
Hereditary Volatility
Hereditary or genotypic variation in biology is the process by which the organism’s genome changes. Thanks to her, an individual acquires features previously unusual for her species. According to Darwin, genotypic variation is the main engine of evolution. The following types of hereditary variation are distinguished:
Combinational variability results from the exchange of genes during sexual reproduction. Moreover, the characteristics of parents are combined in different ways in a series of generations, increasing the diversity of organisms in the population. Combinational variation is subject to Mendel’s inheritance rules.
An example of such variability is inbreeding and outbreeding (closely related and unrelated crossbreeding). When the traits of an individual producer want to be fixed in the breed of animals, then closely related crossbreeding is used. Thus, the offspring becomes more uniform and consolidates the qualities of the founder of the line. Inbreeding leads to the manifestation of recessive genes and can lead to degeneration of the line. Outbreeding is used to increase the viability of offspring - unrelated crosses. In this case, the heterozygosity of the offspring increases and the diversity within the population increases, and, as a result, the resistance of individuals to the adverse effects of environmental factors increases.
Mutations, in turn, are divided into:
- genomic;
- chromosomal;
- gene;
- cytoplasmic.
Changes affecting the germ cells are inherited. Mutations in somatic cells can be transmitted to offspring if an individual propagates vegetatively (plants, fungi). Mutations can be beneficial, neutral, or harmful.
Genomic mutations
Variability in biology through genomic mutations can be of two types:
- Polyploidy - a mutation is often found in plants. It is caused by a multiple increase in the entire number of chromosomes in the nucleus; it is formed in the process of breaking their divergence to the poles of the cell during division. Polyploid hybrids are widely used in agriculture - in plant growing there are more than 500 polyploids (onions, buckwheat, sugar beets, radishes, mint, grapes and others).
- Aneuploidy - an increase or decrease in the number of chromosomes in individual pairs. This type of mutation is characterized by low viability of the individual. A widespread mutation in humans - one extra chromosome in the 21st pair causes Down syndrome.
Chromosomal mutations
Variability in biology through chromosomal mutations appears when the structure of the chromosomes themselves changes: loss of the end region, repetition of a set of genes, rotation of a single fragment, transfer of a segment of a chromosome to another place or to another chromosome. Such mutations often occur under the influence of radiation and chemical pollution of the environment.
Gene mutations
A significant part of such mutations does not appear externally, since it is a recessive trait. Gene mutations are caused by a change in the sequence of nucleotides - individual genes - and lead to the appearance of protein molecules with new properties.
Gene mutations in humans cause the manifestation of certain hereditary diseases - sickle cell anemia, hemophilia.
Cytoplasmic mutations
Cytoplasmic mutations are associated with changes in the cytoplasm structures of cells containing DNA molecules. These are mitochondria and plastids. Such mutations are transmitted through the maternal line, since the zygote receives the entire cytoplasm from the maternal egg. An example of a cytoplasmic mutation that causes variability in biology is plant pinnacle, which is caused by changes in chloroplasts.
All mutations are characterized by the following properties:
- They arise suddenly.
- They are inherited.
- They do not have any focus. Mutations can undergo both an insignificant site and a vital sign.
- Occur in individual individuals, that is, individual.
- In their manifestation, mutations can be recessive or dominant.
- The same mutation can be repeated.
Each mutation is caused by certain reasons. In most cases, it is not possible to precisely establish it. In experimental conditions, to obtain mutations, a directed environmental impact factor is used - radiation exposure and the like.