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 a better chance of adapting to changing environmental conditions.
In a science like biology, heredity and variation go hand in hand. There are two types of variability:
- Non-hereditary (modification, phenotypic).
- Hereditary (mutational, genotypic).
Non-hereditary variability
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 changes in climate and other conditions of existence. Phenotypic variability underlies the adaptive processes occurring in any organism. So, in outbred animals, with the improvement of conditions of detention, productivity increases: milk yield, egg production, and so on. And the animals brought to the mountainous regions grow up short and with good he alth.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 coat color in winter and summer.
The following properties are characteristic of non-hereditary variability:
- group nature of changes;
- not inherited by offspring;
- changing a trait within a genotype;
- The ratio of the degree of change with the intensity of the impact of an external factor.
Hereditary variability
Hereditary or genotypic variability in biology is the process by which the genome of an organism changes. Thanks to her, the individual acquires features that were previously unusual for her species. According to Darwin, genotypic variation is the main engine of evolution. There are the following types of hereditary variability:
- mutational;
- combinative.
Combinative variability results from the exchange of genes during sexual reproduction. At the same time, the traits of the parents are combined in different ways in a number of generations, increasing the diversity of organisms in the population. Combinative variability obeys the rules of Mendelian inheritance.
An example of such variability is inbreeding and outbreeding (closely related andinbreeding). When the traits of an individual producer want to be fixed in the breed of animals, then inbreeding is used. Thus, the offspring becomes more uniform and reinforces the qualities of the founder of the line. Inbreeding leads to the manifestation of recessive genes and can lead to the degeneration of the line. To increase the viability of offspring, outbreeding is used - unrelated crossing. At the same time, 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;
- genetic;
- cytoplasmic.
Changes affecting sex cells are inherited. Mutations in somatic cells can be transmitted to offspring if an individual reproduces vegetatively (plants, fungi). Mutations can be beneficial, neutral or harmful.
Genomic mutations
Variability in biology through genomic mutations can be of two types:
- Polyploidy - mutation is common in plants. It is caused by a multiple increase in the total number of chromosomes in the nucleus, is formed in the process of violation of their divergence to the poles of the cell during division. Polyploid hybrids are widely used in agriculture - in crop production there are more than 500 polyploids (onion, buckwheat, sugar beet, radish, 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 on 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 section, repetition of a set of genes, rotation of a single fragment, transfer of a chromosome segment 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 these mutations does not appear externally, as 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 some hereditary diseases - sickle cell anemia, hemophilia.
Cytoplasmic mutations
Cytoplasmic mutations are associated with changes in the structures of the cell cytoplasm containing DNA molecules. These are mitochondria and plastids. Such mutations are transmitted through the maternal line, since the zygote receives all the cytoplasm from the maternal egg. An example of a cytoplasmic mutation that has caused variability in biology is plant pinnateness, which is caused by changesin chloroplasts.
All mutations have the following properties:
- They appear suddenly.
- Handed down.
- They don't have any direction. Mutations can undergo both an insignificant area 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 causes. In most cases, it cannot be accurately determined. Under experimental conditions, to obtain mutations, a directed factor of the external environment is used - radiation exposure and the like.
