Variability in biology is called nothing more than the properties of organisms to acquire new traits that would differ from their ancestors, as well as individual states of parent organisms compared with descendants during the period of development of an individual organism. The variety of characters among representatives of the same species is also called variability.
Types of variability
The following types of variability are distinguished:
- Inheritable and hereditary. In other words, modification and genetic.
- Individual, which is the difference between individual individuals, and group. The latter consists of changes between entire groups of individuals. This can be, for example, animal populations of the same species. It should be understood that group variability is a derivative of the individual and is also the property of living organisms to acquire new characteristics.
- Distinguish between non-directional and directional variability.
- Quantitative and qualitative.
Due to the properties of organisms to acquire new traits, the emergence of fundamentally new states occurs, which serves as a prerequisite for the subsequent speciation and evolution of the biosphere as a whole. Variability is studied by a science such as genetics. But before turning to the analysis of variability in genetic terms, let us repeat for a more complete understanding of the picture what biological life is as a phenomenon.
Properties of living organisms
Substances from the external environment that provide the vital processes of this organism enter the body. Thanks to nutrition, nutrients and water enter this biological system; respiration provides oxygen. The body processes these substances, partly assimilates, and part takes out, that is, there is a process of excretion. Thus, between the body and the environment there is a metabolism. The intake of nutrients from food provides growth and development; all these processes together are necessary to ensure a very important property of the body - the ability to reproduce.
Any change in environmental conditions immediately causes the corresponding reactions of the body. This is one of the representative indicators of the existence of the properties of organisms to acquire new traits. The main properties of living organisms, namely nutrition, metabolism, growth, respiration, excretion, reproduction, development, irritability, are factors in the existence of a biological unit.
Growth of living organisms
Growth in biology is called the enlargement of the size of the body with an increase in its mass. Plants can be in a state of growth for most of their lives. It is accompanied by an increase in size and the formation of new vegetative organs. Such growth is called unlimited.
The growth of animals is also accompanied by an increase in size - all the organs forming the body of the animal are proportionally increased. But new organs are not formed. The property of organisms to acquire new traits allows the growth of numerous animals to last only a certain period of life, that is, to be limited. Organisms throughout life not only grow, but also develop, change their appearance, acquire new qualities. Development refers to the irreversible regular changes that occur in the organism of living beings from the moment of its inception to the end of life. A new quality that appears in plants and animals during development is the ability to reproduce.
The development of living organisms
Development, in which a new organism from birth is like an adult animal, is called direct. Such development is characteristic of most fish, birds, and mammals. In some animals, development occurs with amazing transformations. For example, in butterflies, larvae hatch from the eggs - caterpillars, which after a while form a pupa. At the pupal stage, complex transformation processes take place, and a new butterfly is already emerging from it. Such development is called indirect, or development with transformations. Indirect development is characteristic of butterflies, beetles, frogs.
Variability in genetics
Genetics is the science of the laws of heredity and variability. In genetics, heredity is the common property of all living organisms to transmit their signs and developmental features to offspring. In turn, variability is the ability of organisms to acquire new traits and properties that are different between individuals within a species. It is difficult to discuss genetic concepts without knowing what a gene is. Therefore, let’s learn that a gene is a part of DNA, the nucleotide sequence of which carries all encoded information necessary for the subsequent synthesis of RNA and polypeptides. A gene is also an elementary unit of heredity.
Alleles are called different variants of a single gene. They arise one above the other as a result of mutations. Contained in identical loci (sites) of homologous chromosomes.
A homozygote is a biological organism that in its cells on homologous chromosomes contains alleles of this gene of only one type.
A heterozygote can be called an organism in which cells in homologous chromosomes contain different alleles of a single gene.
The genotype in genetics is the general set of genes in a biological organism. The phenotype, in turn, is a combination of such body properties that are the result of the interaction of the genotype and the environment.
The role of variability in evolution
The phenotype of each specific living creature is a consequence of the interaction of the genotype of this organism with the conditions that the external environment provides. An impressive part of the variation in the phenotypes of the population is caused by the difference between the genotypes of its individuals. The synthetic theory of evolution defines evolution as a change in this genetic variation. The frequency of alleles in the gene pool fluctuates, as a result of which this allele becomes more or less common in comparison with other forms of such a gene. The general property of all organisms to acquire new characteristics arises in part because evolutionary forces act in such a way that they alter the frequency of alleles. Variation disappears when the frequency of the allele reaches a stationary state.
The occurrence of variation occurs due to mutations of genetic material, migrations among populations and gene shuffling, which occurs as a result of sexual reproduction. You have already learned that the ability of organisms to acquire new traits is called variability, but it is also important to know that it can arise due to the interchange of genes among representatives of more than one species, for example, through gene transfer in a horizontal way in bacteria and hybridization in plants. Despite the constant change in allele frequencies due to these processes, most genomes are almost identical in all individuals of the same species. However, even relatively small changes in the genotype can lead to dramatic changes in the phenotype. For example, the difference between the human genome and the chimpanzee genome is only five percent of the entire DNA chain.