Surprisingly, individuals with a unique, unique genetic device are born every minute 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 single classification unit, but the whole world as a whole. Let's look at what constitutes hereditary variability, what laws it obeys, and how it affects phylogenesis.
Definition
Examples of hereditary variability include certain combinations of the parents' genetic material or various mutational processes during the formation of the zygote. For the most part, the uniqueness of the genotype of various organisms is determined by the divergence of genes in a random order during meiosis.
Inherited Volatility
It is worth noting that, in addition to hereditary variability, non-hereditary also plays a large role in the ontogenesis of the body. It is formed under the influence of the environment, lifestyle and other factors not associated with a change in the genotype. This is precisely the main difference between hereditary and non-hereditary variability.
Mutation Forms
An example of hereditary variation, in addition to the independent movement of chromosomes during the development of the embryo, can also be a certain kind of mutation arising as a result of certain factors. Let's look at each of the forms separately.
Combinative
Combinational variability is one of the main levers of evolution of a certain kind. It is permanent and is found everywhere. Thanks to this type of variability, there is such a phenomenon as the uniqueness of each individual within the species.
Combinational variability is possible due to such phenomena as:
- independent divergence of elementary genetic structures - chromosomes, in the process of meiotic cell division;
- gamete merger randomly in the process of direct fertilization;
- the exchange of genetic material in the process of a phenomenon such as crossing over.
Thus, combinational variability is the main functional unit that ensures the uniqueness of the genetic apparatus of each individual individually.
Mutational
Mutational variation is also an integral part of hereditary processes. Changes can take the form of a useful unique feature of a developing individual, and can be so insignificant that they are not detected at all and are neutral in relation to the body.
But often mutations are negative and manifest themselves in the form of any deviations, violations of the normal functioning of the body, diseases. The danger of negative changes lies in the fact that entrenched in the genotype, they can be inherited.
Also, mutations come in different locations. 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
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 a child with some signs can be very similar to parents. For example, inherit the mother’s dark hair and father’s facial features. This is an example of combinational variability. But it is worth considering that even with 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 variation is the phenomenon of six-fingeredness, which is a consequence of an unforeseen mutation. Or such an unpleasant disease as phenylketonuria, which manifests itself in the form of a violation of amino acid metabolism.
Homological series
One of the scientists who was actively studying the phenomenon of hereditary variability was N.I. Vavilov.
He considered the so-called homologous series of hereditary variability, which were some analogues in the biology of homological series of organic compounds.
Knowing certain patterns, it is possible to calculate the features of inheritance in species that possess these series. On this basis, one of the basic laws was developed that interpreted the laws of inheritance, which is called the law of homological series of hereditary variability. Currently, this law is actively used in genetics.
The law of hereditary variation
This law, formulated on the theory of homologous series, sounds like this: genera and species that have a similar genetic apparatus differ in terms of variability in certain parameters. Based on this, we can conclude that knowing some forms within the same specific 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 specific formula for calculation.
Law Consequences
This law, formulated by N. I. Vavilov, greatly contributes to the interpretation of the characteristics of the evolution of organisms.
So, for example, on its basis, we can conclude that in species that are similar in their genetic apparatus and have a common origin, approximately the same mutational processes can occur. In addition, scientists, as a result of many years of research, have established that even with such large classification units as classes, so-called parallelism based on the presence of homological series can be observed.
It is also worth noting that such phenomena are characteristic not only for the higher classes of living organisms, but for the simplest.
Hereditary diseases
However, as mentioned above, hereditary variability is not always positive for a particular individual and its descendants. For example, various mutations or abnormal behavior of genes in the process of conception and development of the embryo can lead to deviations in the development of individuals of varying degrees of complexity. Consider some types of genetic diseases.
So, hereditary diseases can be divided into:
- Chromosomal These deviations arise as a result of certain changes in the chromosomes. This can be either a change in quantity or in the structure itself. Down syndrome is considered the most common disease in this group. Children suffering from this syndrome differ in its severity, but with the corrective and medical care, in the future they can be completely socialized and independent.
- Genomic. Mutations of this type, affecting the entire genome completely, 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 other symptoms, are characterized by poor mental health and mild or mild sexual characteristics.
- Monogenic. The basis of these diseases is a mutation in one specific gene. It can be either dominant or recessive. Some mutations are sex-linked, some are autosome-linked.
Hereditary variation 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 preserve the uniqueness of genetic material and adapt to the characteristics of a particular environment, the organisms of any organization would be doomed to death.
Due to hereditary variation, there is such an important evolutionary factor as natural selection. Due to the fact that each individual is unique in its genotypic and phenotypic properties, 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. Indeed, it is precisely 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 varying environmental features force organisms to adapt to existing conditions. Without this or that reflection in the genotype, this would have been impossible and led to the extinction of the species.