It's amazing, but every minute individuals with a unique, unique genetic makeup are born on Earth. This is due to a certain hereditary variability, the value of which is large enough for the evolutionary development of not only a separate classification unit, but the whole world as a whole. Let's see what hereditary variability is, what laws it obeys and how it affects phylogeny.
Examples of hereditary variability are certain combinations of the genetic material of the parents or various mutational processes during the formation of the zygote. For the most part, the uniqueness of the genotype of various organisms is due to the divergence of genes in a random order during meiosis.
It is worth noting that in addition to hereditary variability, non-hereditary also plays an important role in the ontogeny of the organism. She isis formed under the influence of the environment, lifestyle and other factors not related to changes in the genotype. This is precisely the main difference between hereditary and non-hereditary variability.
An example of hereditary variability, in addition to the independent movement of chromosomes in the development of the embryo, can also be a certain kind of mutation resulting from certain factors. Let's look at each of the forms separately.
Combinative variability is one of the main levers of the evolution of a certain species. It is permanent and occurs everywhere. It is thanks to this type of variability that there is such a thing as the uniqueness of each individual within a species.
Combination variability is possible due to phenomena such as:
- independent divergence of elementary genetic structures - chromosomes, in the process of meiotic cell division;
- fusion of gametes randomly during direct fertilization;
- exchange of genetic material in the process of such a phenomenon as crossing over.
Thus, combinative variability is the main functional unit that ensures the uniqueness of the genetic apparatus of each individual separately.
Mutational variability is also an integral part of hereditary processes. Changes can take the form of a useful unique feature of the developing individual, andmay be so insignificant that they are not detected at all and are neutral in relation to the organism.
But often mutations are negative and manifest themselves in the form of any deviations, disturbances in the normal functioning of the body, diseases. The danger of negative changes lies in the fact that once they are fixed in the genotype, they can be inherited.
Also, mutations come in different localizations. On this basis, they are divided into somatic and generative. They affect different levels of the genetic apparatus, which classifies them as chromosomal, gene or genomic.
Examples of hereditary variability are very diverse and often found in everyday life. One of the most elementary manifestations of this type of variability is that the child may be very similar to the parents in some respects. For example, to inherit the dark hair of the mother and the facial features of the father. This is an example of combinative variability. But it is worth considering that even with a strong similarity, the offspring will not be an exact copy of the parents, both in phenotypic and, especially, in genotypic terms.
Another example of hereditary variability is the phenomenon of six-fingeredness, which is the result of an unforeseen mutation. Or such an unpleasant disease as phenylketonuria, which manifests itself in the form of a violation of amino acid metabolism.
One of the scientists whoactively engaged in the study of such a phenomenon as hereditary variability, was N.I. Vavilov.
He considered the so-called homological series of hereditary variability, which were some analogues in the biology of the homological series of organic compounds.
Knowing certain patterns, it is possible to calculate the features of inheritance in species that have these series. On this basis, one of the basic laws was formed that interprets the patterns of inheritance, which is called the law of homologous series of hereditary variability. At the moment, this law is actively used in genetics.
The law of hereditary variability
This law, formulated on the theory of homologous series, sounds like this: genera and species that have a similar genetic apparatus differ in the series of variability in certain parameters. Based on this, we can conclude that knowing some forms within one particular species, one can predict the presence of the same forms in similar species.
N. I. Vavilov reinforced the law of homological series of hereditary variability with a certain formula for calculation.
Consequences of the law
This law, formulated by N.I. Vavilov, largely contributes to the interpretation of the features of the evolution of organisms.
So, for example, based on it, we can conclude that in species that are similar in their genetic apparatus and have a common origin, approximately the same mutation processes can occur. Besides,scientists, as a result of many years of research, have established that even such large classification units as classes can experience the so-called parallelism based on the presence of homologous series.
It is also worth noting that such phenomena are typical not only for the higher classes of living organisms, but for the simplest ones.
However, as mentioned above, hereditary variability does not always have a positive effect for a particular individual and its descendants. For example, various kinds of mutations or non-standard behavior of genes in the process of conception and development of the embryo can lead to deviations in the development of an individual of varying degrees of complexity. Consider some types of genetic diseases.
So, hereditary diseases can be divided into:
- Chromosomal. These deviations occur as a result of certain changes in chromosomes. It can be both a change in the quantity and the structure itself. Down syndrome is considered the most common disease of this group. Children suffering from this syndrome differ in its severity, but with proper corrective and medical care, they can be fully socialized and independent in the future.
- Genomic. Mutations of this type, affecting the entire genome, occur less frequently and almost always lead to death in animals and humans in particular. An example of such a disease is Shereshevsky-Turner syndrome. People with this syndrome, in addition to many otherssigns are characterized by poor mental he alth and mild or obliterated sexual characteristics.
- Monogenic. These diseases are based on a mutation in one particular gene. It can be either dominant or recessive. Some mutations are sex-linked, some are autosome-linked.
Hereditary variability in evolution
Variability is the main and very important property of living organisms to undergo changes in the process of phylogenesis. Without such a feature that allows you to maintain the uniqueness of the genetic material and adapt to the characteristics of a particular environment, the organisms of any organization would be doomed to death.
Due to hereditary variability, there is such an important factor in evolution as natural selection. It is precisely because each individual is unique in its genotypic and phenotypic properties that the number is regulated in nature, but at the same time, it remains possible to avoid the complete disappearance of one or another classification unit.
The value of hereditary variation is invaluable to the evolutionary process. After all, it is this most important feature of organisms of any complexity and classification that allows such a phenomenon as species diversity to exist. Also, hereditary variability is of great importance for the survival of the species. Constantly changing features of the environment force organisms to adapt to the existing conditions. Without this or that reflection in the genotype, this would be impossible andled to the extinction of the species.