People have always been interested in patterns.trait inheritance. Why do children resemble their parents? Is there a risk of transmission of hereditary diseases? These and many other questions remained under a veil of secrecy until the XIX century. It was then that Mendel managed to accumulate all the accumulated knowledge on this topic, as well as to establish specific patterns through complex analytical experiments.
Mendel's contribution to the development of genetics
The main patterns of inheritance of characters -these are principles according to which certain characteristics are passed from parent organisms to offspring. Their discovery and clear wording is a merit of Gregor Mendel, who conducted numerous experiments on this issue.
The main achievement of the scientist is proofdiscrete nature of hereditary factors. In other words, a specific gene is responsible for each trait. The first maps were built for corn and fruit flies. The latter is a classic object for conducting genetic experiments.
Mendel's merits can not be overemphasized what they sayand domestic scientists. Thus, the famous geneticist Timofeev-Resovsky noted that Mendel was the first to conduct 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 inheritancesigns by Mendel were not formulated from scratch. His research was based on the research of predecessors. It is especially worth noting the following scientists:
- J.Goss conducted experiments on peas, crossing plants with fruits of different colors. It was 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.
- Огюстен Саржэ - это растениевод, выбравший для their experiences pumpkin culture. He first began to study hereditary traits not in the aggregate, but separately. He claims that when transferring certain characteristics, they do not mix with each other. Thus, heredity is constant.
- Nodeden conducted research on various typessuch a plant as a dope. After analyzing the results, he found it necessary to talk about the presence of dominant traits, which in most cases will prevail.
Thus, by the XIX century suchphenomena like dominance, uniformity of the first generation, as well as combinatorics of traits in subsequent hybrids. Nevertheless, no general laws were worked out. It is the analysis of the available information and the development of a reliable research methodology that are the main achievements of Mendel.
Methodology of Mendel
The patterns of inheritance of traits according to Mendel were formulated as a result of fundamental research. The activities of the scientist was carried out as follows:
- hereditary traits were considered not in the aggregate, but separately;
- Only alternatives were selected for analysis.traits that represent a significant difference between species (this is what made it possible to most clearly explain the patterns of the inheritance process);
- the research was fundamental (Mendelinvestigated a large number of pea varieties that were both pure and hybrid, and then crossed the "offspring"), which allowed to speak about the objectivity of the results;
- the use of accurate quantitative methods in the analysis of the obtained data (using knowledge in the field of probability theory, Mendel reduced the rate of random deviations).
The law of uniformity of hybrids
Considering patterns of inheritancesigns, it is worth paying special attention to the uniformity of hybrids of the first generation. It was discovered by experience, during which the parental forms were crossed with one contrasting sign (form, color, etc.).
Mendel decided to holdAn experiment on two pea varieties - with red and white flowers. As a result, hybrids of the first generation received purple inflorescences. Thus, there is reason to talk about the presence of dominant and recessive traits.
It is worth noting that this experience of Mendel was notthe only one. He used for experiments plants with different shades of inflorescences, with different shape of fruits, different stem height and other options. By experiment, he was able to prove that all hybrids of the first order are uniform and characterized by a dominant trait.
Incomplete dominance
In the course of studying such an issue aspatterns of inheritance of traits, experiments were carried out both on plants and on living organisms. Thus, it was possible to establish that the signs are not always in a relationship of complete domination and suppression. For example, when crossing chickens of black and white color, it was possible to get gray offspring. It was the same with some plants, when varieties with purple and white flowers gave pink shades at the exit. Thus, it is possible to correct the first principle, indicating that the first generation of hybrids will have the same characteristics, while they may be intermediate.
Splitting signs
Continuing to explore patterns of inheritancesigns, Mendel found it necessary to cross the two descendants of the first generation (heterozygous). As a result, offspring was obtained, part of which bore the dominant trait, and the other - recessive. From this we can conclude that the secondary trait 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
Много вопросов вызывают закономерности trait inheritance. The experiments of Mendel also touched individuals, which differ from each other at once on several grounds. For each individually, the previous patterns were respected. But now, considering the totality of signs, it was not possible to identify any patterns between their combinations. Thus, there is reason to talk about the independence of inheritance.
The law of purity of gametes
Some patterns of inheritance of traitsestablished by Mendel, were purely hypothetical. We are talking about the law of purity of gametes, which consists in the fact that only one allele from a pair contained in the gene of the parent individual enters them.
At the time of Mendel there was no technical means.to confirm this hypothesis. Nevertheless, the scientist was able 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 not mixed.
Essential conditions
Genetics is a science that studies patterns.trait inheritance. Mendel made a significant contribution to its development by developing the fundamental provisions on this issue. However, in order for them to be fulfilled, the following essential conditions must be met:
- original forms must be homozygous;
- alternativeness of features;
- the same probability of the formation of different alleles in a hybrid;
- equal viability of gametes;
- during fertilization, gametes are combined randomly;
- zygotes with different combinations of genes are equally viable;
- the number of individuals of the second generation should be sufficient to consider the results obtained as logical;
- manifestation of signs should not be dependent on the influence of external conditions.
It should be noted that most of the living organisms, including humans, correspond to these characteristics.
Patterns of inheritance of traits in humans
Despite the fact that initially genetic principles were studied using plants as an example, for animals and humans they are also valid. It is worth noting the following types of inheritance:
- Аутосомно-доминантный - наследование доминирующих traits that are localized through autosomes. In this case, the phenotype can be both strongly pronounced and barely 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 to autosomes. Diseases are manifested through homozygotes, and both alleles will be affected.
- The dominant X-linked type implies the transfer of dominant traits by deterministic genes. At the same time, in women, the diseases occur 2 times more often than in men.
- Recessive X-linked type - inheritanceoccurs on a weaker basis. The disease or its individual signs are always manifested in male offspring, and in women only in the homozygous state.
Basic concepts
In order to understand how the patterns of inheritance of Mendel signs and other genetic processes work, it is worth getting acquainted with the basic definitions and concepts. These include the following:
- The dominant trait is the predominant characteristic that acts as the determining state of the gene and suppresses the development of recessive ones.
- Recessive trait - a characteristic that is inherited, but does not act as a defining one.
- A homozygote is a diploid individual or a cell whose chromosomes contain identical cells of the indicated gene.
- A heterozygote is a diploid individual or cell that splits and has different alleles within a single gene.
- Allele is one of the alternative forms of the gene, which is located in a specific place of the chromosome and is characterized by a unique nucleotide sequence.
- An allele is a pair of genes that are located in the same zones of homologous chromosomes and control the development of certain traits.
- Nonallelic genes are located on different parts of the chromosomes and are responsible for the manifestation of various signs.
Conclusion
Mendel formulated and proved in practicethe main 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.
