Heredity and variability are the basic conditions of the evolutionary process. Both of these opposing features are inseparable and are included in the characteristics of all living organisms. Almost the entire history of the science of biology was based on the study of the interaction and significance of these features. Even in ancient Greece, attempts were made to comprehend the diversity of organisms. Plato, Anaximenes, Heraclitus and many others argued that everything in nature changes as a result of internal struggle. What laws of variability and heredity exist? This issue has been studied by many scientists for a long time.
Sustainable properties of living organisms
Even in antiquity, there were suggestions about the inherent variability and heredity inherent in living beings. Attention was drawn to the fact that during reproduction from one generation to another, a number of characters are transmitted that are typical for this species. This has been called heredity.
Along with this, there are some differences between representatives of the same species, which was called variability. Patterns of heredity and variability were already applied then to create other breeds of animals and plant varieties thanks to G. Mendel, who after many experiments managed to describe them. In 1900, a new science began to develop - genetics, which studies the laws of these two fundamental properties of organisms.
The concept of genetics
Heredity is the totality of traits that organisms repeat from generation to generation. A special role is given to physiology, chemical composition, external structure and the nature of the metabolic processes of organisms. Variability refers to a phenomenon that is the opposite of heredity and is expressed in a change in the complex of characters or the formation of new properties in organisms of the same species. The combination of these two properties contributes to evolution, as a result of which new characters are formed in individuals, which are preserved in the next generation.
A large number of new traits leads to the formation of new species. That is why genetics is aimed at studying the laws of variability and heredity in order to understand the development of evolution, to create new types of living organisms that are more adapted to constantly changing environmental conditions.
Variability and its laws
In genetics, it is customary to distinguish between hereditary (genotypic) and modification variability. Genotypic variation is characterized by the change in traits that determines the genotype and which lasts several generations. Non-hereditary variability is characterized by those changes in traits that are caused by the influence of the external environment and are inherited from parents to offspring. It does not concern the hereditary base of the body - the genotype - but is prone to be transmitted.
The patterns of modification variability lie in the fact that it has a group orientation. For all representatives of a certain type, environmental circumstances contribute to similar changes. Modifications have a direction, unlike mutations, they are subject to patterns, so they can be predicted. For example, with leaves blossoming on trees, the air temperature at night was negative, as a result of which in the morning all of them will acquire a reddish hue. Thanks to the modifications, individuals have an adequate reaction to changes in environmental factors, so they adapt to it faster in order to survive and leave offspring.
Reaction rate
Non-hereditary variation is subject to patterns. The statistical laws of modification variability lie in the fact that its boundaries depend on the genotype, they are called the reaction norms (NR). It has boundaries for each of the signs. Narrow HP determines the signs on which the viability of the organism depends, and wide HP plays an important role in saving the species.
Most likely, an individual inherits the ability of his genotype due to interaction with the environment to create a specific phenotype. Also, the statistical laws of non-hereditary variability determine the presence of traits that determine the genotype almost in full. For example, the number of limbs, the location of the eyes, and so on.
The determination of quantitative traits is influenced by the environment. In order to study the variability of a particular trait, geneticists compile a so-called variational series, which consists of sequential quantitative indicators of a particular trait that are arranged in increasing or decreasing order. The length of this series indicates the boundaries of non-hereditary variability; it depends on the stability of environmental conditions.
The body is an open construction, heredity is realized here through the interaction of the genotype with the environment. Representatives of the same genotypes under different environmental conditions can form different phenotypes.
Hereditary variability
Hereditary is divided into mutational (MI) and combined (CI). Here the main laws of variability come into force. CI is characterized by the fact that, when mating gametes that are different from each other in genotype, new genotypes appear, which parents did not have. For example, children never repeat their parents completely, they get a genotype that consists of a combination of genes from two ancestors. This happens in four ways. The first way is the separation of chromosomes during reduction cell division, the second is the physical exchange of chromosome sites in meiosis, and the third way is involuntary gamete combinations during fertilization, and the last is gene interaction.
Mutational heredity
Mutations are transformations of the genotype, including whole chromosomes or individual genes that occur randomly and are persistent. They are large (albinism, short-bore, etc.) and small. They are also divided into several types: genomic, chromosomal and gene mutations.
Genome and chromosome mutations
This type of mutation is characterized by a change in the number of chromosomes. In some individuals, polyploidy is observed - a change in the multiple number of chromosomes. So, in such organisms, the chromosome set in the cells is repeated not two, but much more times. This occurs as a result of a disturbance in the course of mitosis or meiosis, when the division chain is destroyed, the double chromosomes do not diverge, but remain inside the cell, as a result of which gametes with a double set of information are formed. If such a gamete merges with normal, then the offspring will have a triple number of chromosomes.
On this, the laws of variability are not exhausted. It happens that the chromosome rearrangement is observed in an individual. Some of its sections change their position, they are either lost or doubled. This is the mutation of chromosomes.
Gene mutations
This type of mutation is associated with a change in the composition or order of nucleotides within the boundaries of the gene. It can be lost or replaced by another, the formation of an excess nucleotide can also be observed. Such mutations cause the gene to stop functioning, as a result of which certain RNA and protein do not appear, or the protein acquires other properties, which leads to a change in the phenotype. Gene mutations are very important because with their help new alleles appear.
Somatic and gene mutations
The patterns of organisms' variability also lie in the fact that some mutations occur only in the reproductive cells, therefore phenotypes are formed only in the offspring. They are called generative.
In cells, somatic mutations can also form. In this case, they are not transmitted to descendants during reproduction. But if reproduction is asexual, then mutations can be transmitted to offspring. They are called somatic.
Mutation Properties
Mutations tend to be inherited steadily. Their significance in the process of evolution is very great. The patterns of variability lie in the fact that only hereditary mutations can be passed on to the next generations if they multiply safely and survive with these traits.
All changes can be caused by both external and internal factors. Temperature jumps, cell fading, the influence of various substances, ultraviolet radiation - all this can provoke DNA mutations and even chromosomes.
Changes appear suddenly, in some cases it is harmful to the body, because they interfere with the genotype, which was established a large amount of time. Mutations have no direction, they can be repeated, and any gene can undergo a change, leading to the transformation of both small and vital signs. One and the same environmental factor can lead to a variety of changes that are almost impossible to foresee. Therefore, genetics is important for us today, the laws of variability and heredity play a significant role in the evolution process.
Thus, genes are carriers of hereditary information . Moreover, a particular gene is responsible for certain traits. The latter determines any quality of the body: physiological, biochemical or morphological. By this quality, one living creature is distinguished from another. The complex of genes is called the genotype, and the complex of traits is called the phenotype.
In nature, there are certain laws of variability and heredity, due to which living organisms adapt to rapidly changing environmental conditions. Mutations can form on different parts of the DNA, affect genes and chromosomes. As a result of this, we have a huge classification of living organisms.