Did you know that modification variation, unlike mutational variation, is driven solely by environmental factors? Which of these changes is more important for the adaptation of organisms? You will find answers to these and many other questions in our article.
Variability of organisms: meaning
Variability is a universal biological phenomenon. Its essence lies in the ability of organisms to acquire new features in the process of individual development. The result of variability is the emergence of new characters and species. And with a global consideration - the development of the biosphere as a whole. Variability is a factor in evolution, provides the ability of organisms to adapt, genetic diversity and material for selection.
Appearance of modifications
One of the main areas of genetics is to elucidate the mechanisms of interaction of the genotype with the environment. It has long been known that if two identical individuals develop in different conditions, they have a number of external differences. This is a manifestation of non-hereditary, or modification variability. The study of this property of living organisms allows us to determine how hereditary traits manifest themselves in given conditions.
Modification variability, in contrast to mutational variability, is a response to the intensity of certain factors. Non-hereditary changes are the same for all genotypically homogeneous creatures. Proof of this is the arrowhead, whose leaves in the water are leaf-shaped, and on land - arrow-shaped. Such changes protect the plant from damage by the current.
In the case of modification variability, new traits do not cause changes in the genetic material. So, if the tails of mice are cut off, tailed offspring will be born. Such an experiment was first conducted by the German scientist August Weismann.
Normally modifications disappear when the factor causing them stops. So, summer tan by the autumn-winter period is almost invisible. But in some cases, such signs persist throughout life or are even inherited in a number of generations. For example, at high temperatures, messenger RNA molecules accumulate in the cells of the Colorado potato beetle pupae, which determine the dark color. But from generation to generation, the number of these molecules decreases, and the trait gradually disappears.
Reaction rate
Modification variability, inUnlike mutational variability, it obeys certain statistical patterns. Its limits are called the reaction norm. A narrower reaction rate is characteristic of the traits that determine viability. For example, the relative position of internal organs. For signs that are not so important, it can be wider.
Causes of mutations
Mutational variability, in contrast to modification, arises as a result of the formation of new structures in the genotype of organisms. They are called mutations. Such modifications can be of a different nature. Mutations can be associated with a change in the number or structure of chromosomes, the number of chromosome sets, as well as with a violation of the sequence of nucleotides in nucleic acid molecules. In any case, there is a violation of the hereditary programs of cells and the body as a whole. As a result - a change in the phenotype, which is not always beneficial for individuals.
Modifications and mutations: traits for comparison
All types of variability are the source of evolutionary neoplasms and a universal property of living matter. But modification variability, unlike mutational variability, is not inherited and does not affect DNA. The body acquires new features of the external structure, which are useful in certain conditions.
Mutational variability, in contrast to modification, is uncertain. It is impossible to determine in advance exactly what signs will appear in the body. Modifications are predictable. And they will be the same for all organisms from the group. For example, if several rabbits are placed in conditions of low temperature, they will all change color. If you irradiate a bag of seeds, mutations will appear in everyone, but they will be completely different.
The vast majority of modifications are adaptive. Sunburn appears to protect the skin from the harmful effects of solar radiation, the thick coat of animals during the autumn molt - from the effects of cold. Although this does not always happen. So, if you shade the lower part of the potato shoot, above-ground tubers will begin to appear. Mutations can be harmful, neutral or beneficial.
So, variability is the universal ability of all living things to acquire new features. Mutational variability, in contrast to modification, is due to sudden changes in the genetic material and is inherited.
