variability in biology - is the emergence of individual differences between individuals of the same species.Due to the variability of the population becomes heterogeneous, and the species have more chances to adapt to changing environmental conditions.
In this science, biology, heredity and variability of go hand in hand.There are two types of variability:
- non-hereditary (Modification, phenotypic).
- Hereditary (mutation, genotype).
non-hereditary variability
Modification variability in biology - the ability of a single living organism (phenotype) to adapt to environmental factors within its genotype.Due to this property, individuals adapt to climate change and other conditions of existence.Phenotypic variation is the basis of adaptation processes occurring in any organism.Thus, in outbred animals by improving the conditions of increased productivity: milk production, egg production, and so on.And animals imported into the mountainous areas grow stunted and with a well developed undercoat.Changing environmental factors and cause variability.Examples of this process can be easily found in everyday life: the human skin is exposed to ultraviolet light becomes dark, as a result of physical exertion muscles develop, plants grown in shaded areas and on light, have different shapes of leaves, and the hares change color wool in winter and summer.
For non-hereditary variability characterized by the following properties:
- group character changes;
- not inherited by the offspring;
- change feature within genotype;
- ratio of the rate of change with the intensity of the impact of external factors.
Hereditary variability
Hereditary or genotypic variability in biology - is the process by which changes the genome of an organism.Thanks to the individual acquires the characteristics previously uncharacteristic of her mind.According to Darwin, genotypic variability is the main engine of evolution.The following types of genetic variation:
- mutation;
- combinative.
combinative variability arises from the exchange of genes in sexual reproduction.Thus signs parents differently combined in a number of generations, increasing the diversity of organisms in the population.Combinative variability follows the rules of Mendelian inheritance.An example of such variability - inbreeding and outbreeding (closely related and unrelated mating).When the features of the individual producer wants to fix in the breed of the animal, then the inbreeding.Thus, the offspring becomes more uniform and establishes as the founder of the line.Inbreeding leads to the expression of recessive genes, and can lead to degeneration of the line.To improve the viability of the progeny used outbreeding - outbreeding.This increases the offspring heterozygosity and increased diversity within the population, and as a result, increases the stability of individuals to adverse environmental factors.
mutations, in turn, are divided into:
- genome;
- chromosome;
- gene;
- cytoplasmic.
Changes affecting germ cells, are inherited.Mutations in somatic cells can be transmitted to offspring, if the individual is vegetatively propagated (plants, fungi).Mutations can be beneficial, neutral or detrimental.
genomic mutations
variability in biology through genomic mutations can be of two types:
- Polyploidy - a mutation commonly found in plants.It is caused by a magnification of the total number of chromosomes in the nucleus is formed in violation of their differences to the poles of the cell during division.Polyploid hybrids are widely used in agriculture - crop production has more than 500 polyploids (onions, buckwheat, sugar beets, radishes, mint, grapes, etc.).
- Aneuploidy - increase or decrease in the number of chromosomes of individual couples.This type of mutation is characterized by low viability of the individual.The widespread mutation in humans - one extra chromosome on the 21st pair causes Down syndrome.
chromosomal mutations
variability in biology by chromosomal mutation occurs when changes in the structure of chromosomes: the loss of the end portion, the repetition of a set of genes that turn a separate piece, the transfer of a segment of the chromosome to another location or to a different chromosome.Such mutations are often caused by exposure to radiation and chemical pollution.
Gene mutations
A significant portion of these mutations does not appear outwardly as a recessive trait.Gene mutations due to a change in the sequence of nucleotides - individual genes - and lead to the appearance of protein molecules with novel properties.Gene mutations in humans cause some manifestation of hereditary diseases - sickle cell anemia, hemophilia.
cytoplasmic mutation cytoplasmic
mutations are associated with changes in the structures of the cytoplasm of cells containing the DNA molecule.This mitochondria and plastids.Such mutations are transmitted through the maternal line, as the zygote gets all the cytoplasm of the egg from the mother.Example cytoplasmic mutations caused by the variability in biology - is peristolistnost plant, which is caused by changes in the chloroplasts.
All mutations characterized by the following properties:
- They occur suddenly.
- inherited.
- They do not have any direction.Mutations may be exposed as insignificant portion, and vital signs.
- occurs in some individuals, that is individual.
- in its manifestation mutations can be dominant or recessive.
- The same mutation can be repeated.
Each mutation caused by certain factors.In most cases, to ascertain it fails.The experimental conditions used to produce mutations aimed factor external environment - radiation exposure, and the like.
