The basic patterns of inheritance of characters, established by G. Mendel: description and functions

People have always been interested in patterns of inheritance of characters. Why do children look like their parents? Is there a risk of transmission of hereditary diseases? These and many other issues remained under the veil of mystery until the XIX century. It was then that Mendel succeeded in accumulating all the accumulated knowledge on this topic, and also through establishing complex analytical experiments to establish specific patterns.

Mendel's contribution to the development of genetics

The basic patterns of inheritance of characteristics are the principles according to which certain characteristics are transferred from the parent organisms to the offspring. Their discovery and clear formulation is the merit of Gregor Mendel, who conducted numerous experiments on this issue.

The main achievement of the scientist is the proof of the discrete nature of hereditary factors. In other words, a specific gene is responsible for each attribute. The first maps were built for corn and Drosophila. The latter is a classical object for carrying out genetic experiments.

Merits of Mendel can not be overestimated, as domestic scientists say. So, the famous geneticist Timofeev-Resovsky noted that Mendel was the first who conducted fundamental experiments and gave an accurate description of phenomena that previously existed at the level of hypotheses. Thus, it can be considered a pioneer of mathematical thinking in the field of biology and genetics.

Predecessors

It is worth noting that the patterns of inheritance of features according to Mendel were formulated not in an empty place. His research was based on the research of his predecessors. It is worth mentioning especially the following scientists:

• J. Goss experimented on peas, crossing plants with fruits of different colors. It is thanks to these studies that the laws of uniformity of the first generation of hybrids, as well as incomplete dominance, were discovered. Mendel only concretized and confirmed this hypothesis.
• Augustin Sarge is a plant grower who has chosen pumpkin cultures for his experiments. He was the first to study hereditary traits, not in aggregate, but separately. He claims that they do not mix with each other when they transmit certain characteristics. Thus, heredity is constant.
• Noden conducted research on various species of such plants as dope. Analyzing the results, he found it necessary to talk about the presence of dominant signs, which in most cases will prevail.

Thus, by the XIX century, such phenomena as dominance, uniformity of the first generation, as well as combinatorics of attributes in the subsequent hybrids were known. Nevertheless, there were no universal laws. It is precisely the analysis of the available information and the development of a reliable research methodology that are the main merit of Mendel.

Mendel's methods of work

Patterns of inheritance of signs by Mendel were formulated as a result of fundamental research. The activity of the scientist was carried out as follows:

• Hereditary traits were not considered in the aggregate, but separately;
• For the analysis, only alternative features were selected that represent a significant difference between the varieties (this is what made it possible to explain the regularities of the inheritance process most clearly);
• Studies were fundamental (Mendel investigated a large number of varieties of peas that were both pure and hybrid, and then crossed the "offspring"), which allowed to speak about the objectivity of the results;
• The use of precise quantitative methods in the analysis of the data obtained (using knowledge in the field of probability theory, Mendel reduced the index of random deviations).

The law of uniformity of hybrids

Considering the patterns of inheritance of features, it is worth paying special attention to the uniformity of hybrids of the first generation. It was discovered by experience, in the course of which the crossing of parental forms with one contrast sign was made (form, color, etc.).

Mendel decided to conduct an experiment on two varieties of peas - with red and white flowers. As a result, hybrids of the first generation received purple inflorescences. Thus, there was a basis for talking about the presence of dominant and recessive traits.

It is worth noting that this experience Mendel was not the only one. He used for experiments plants with other shades of inflorescences, with different forms of fruits, different heights of the stem and other variants. Experienced, he managed to prove that all hybrids of the first order are uniform and characterized by a dominant feature.

Incomplete dominance

In the course of studying such a question as the patterns of inheritance of traits, experiments were carried out both on plants and on living organisms. Thus, it was possible to establish that not always the signs are in a relationship of total domination and suppression. For example, when crossing black and white chickens, it was possible to obtain gray offspring. So it was with some plants, when varieties with purple and white flowers at the outlet gave pink shades. Thus, the first principle can be corrected, indicating that the first generation of hybrids will have the same characteristics, and they may be intermediate.

Splitting features

Continuing to investigate the patterns of inheritance of characters, Mendel found it necessary to cross two offspring of the first generation (heterozygous). As a result, the offspring were received, some of which were dominant, and the other was recessive. From this it can be concluded that the secondary sign of the first generation of hybrids does not disappear at all, but is only suppressed and may well manifest itself in subsequent offspring.

Independent inheritance

Many questions raise the patterns of inheritance of traits. Experiments Mendel also touched individuals, which differ from each other on several grounds. For each individual, the previous patterns were observed. But, considering the set of characteristics, it was not possible to reveal any patterns between their combinations. Thus, there is reason to talk about the independence of inheritance.

Law of purity of gametes

Certain patterns of inheritance of characters, established by Mendel, were purely hypothetical. It is a question of the law of the purity of gametes, which consists in the fact that they contain only one allele from the pair contained in the gene of the parent.

In the time of Mendel, there was no technical means to confirm this hypothesis. Nevertheless, the scientist managed to formulate a general statement. Its essence lies in the fact that in the process of the formation of hybrids, hereditary characteristics remain unchanged, and do not mix.

Essential conditions

Genetics is a science that studies the patterns of inheritance of characters. Mendel made a significant contribution to its development, having developed fundamental provisions on this issue. Nevertheless, in order for them to be fulfilled, the following essential conditions must be observed:

• The original forms must be homozygous;
• Alternativeness of signs;
• The same probability of formation of different alleles in the hybrid;
• Equal viability of gametes;
• When fertilized gametes are combined at random;
• Zygotes with different combinations of genes are equally viable;
• The number of individuals of the second generation should be sufficient to take the results as legitimate;
• The manifestation of features should not be dependent on the influence of external conditions.

It is worth noting that most of the living organisms, including humans, correspond to these characteristics.

Patterns of inheritance of traits in humans

In spite of the fact that the genetic principles were initially investigated using plants as an example, they are also valid for animals and humans. It is worth noting such types of inheritance:

• Autosomal dominant is the inheritance of dominant traits that are localized through autosomes. In this case, the phenotype can be either very pronounced or hardly noticeable. With this type of inheritance, the probability of a child receiving a pathological allele from the parent is 50%.
• Autosomal recessive - inheritance of secondary signs connected with autosomes. Diseases are manifested through homozygotes, and both alleles are affected.
• The dominant X-linked type implies the transfer of dominant features to deterministic genes. At the same time, women are twice as likely to have diseases as men.
• Recessive X-linked type - inheritance occurs on a weaker basis. The disease or its individual signs always appear in the offspring of the male sex, and in women only in the homozygous state.

Basic concepts

In order to understand how the patterns of inheritance of Mendel's features and other genetic processes work, it is worth familiarizing themselves with the basic definitions and concepts. These include the following:

• The dominant feature is the predominant characteristic that acts as the determining state of the gene and inhibits the development of recessive ones.
• A recessive attribute is a characteristic that is inherited, but does not act as a defining feature.
• Homozygote - a diploid individual or cell, in the chromosomes of which the same cells of the gene are contained.
• A heterozygote is a diploid individual or a cell that splits and has different alleles within the same gene.
• Allele is one of the alternative forms of the gene that is located at a specific place of the chromosome and is characterized by a unique sequence of nucleotides.
• Allele is a pair of genes that are located in the same zones of homologous chromosomes and control the development of certain traits.
• Non-allelic genes are located on different sections of chromosomes and are responsible for the manifestation of various traits.

Conclusion

Mendel formulated and in practice proved the basic patterns of inheritance of characters. Their description is given on the example of plants and slightly simplified. But in practice it is fair for all living organisms.