People have always been interested in patterns of trait inheritance. Why do children look like their parents? Is there a risk of transmission of hereditary diseases? These and many other questions remained under a veil of secrecy until the 19th century. It was then that Mendel managed to accumulate all the accumulated knowledge on this topic, and also, through complex analytical experiments, to establish specific patterns.
Mendel's contribution to the development of genetics
Basic patterns of inheritance of traits are the principles according to which certain characteristics are transmitted from parent organisms to 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 trait. The first maps were built for corn and Drosophila. The latter is a classic object for genetic experiments.
Mendel's merits can hardly be overestimated, as Russian scientists also talk about. Thus, the famous geneticist Timofeev-Resovsky noted that Mendelwas the first who conducted fundamental experiments and gave an accurate description of the phenomena that previously existed at the level of hypotheses. Thus, he can be considered a pioneer of mathematical thinking in the fields of biology and genetics.
Precursors
It is worth noting that the patterns of inheritance of traits according to Mendel were not formulated from scratch. His research was based on the research of his predecessors. Of particular note are the following scholars:
- 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.
- Augustin Sarger is a grower who chose cucurbits for his experiments. He was the first to study hereditary traits not in aggregate, but separately. He owns the assertion that when transferring certain characteristics, they do not mix with each other. Thus, heredity is constant.
- Noden conducted research on various types of such a plant as Datura. After analyzing the results, he considered it necessary to talk about the presence of dominant features, which in most cases will prevail.
Thus, already by the 19th century such phenomena as dominance, uniformity of the first generation, as well as combinatorics of characters in subsequent hybrids were known. However, no general patterns have been developed. It is the analysis of the existinginformation and the development of a reliable research methodology are the main merit of Mendel.
Mendel's workflow
The patterns of inheritance of traits according to Mendel were formulated as a result of fundamental research. The activity of the scientist was carried out as follows:
- hereditary traits were considered not in aggregate, but separately;
- only alternative traits were selected for analysis, which represent a significant difference between the varieties (this is what made it possible to most clearly explain the patterns of the inheritance process);
- research was fundamental (Mendel studied a large number of pea varieties that were both pure and hybrid, and then crossed "offspring"), which made it possible to speak about the objectivity of the results;
- use of precise quantitative methods in the course of data analysis (using knowledge of probability theory, Mendel reduced the rate of random deviations).
Law of Uniformity of Hybrids
Considering the patterns of inheritance of traits, it is worth paying special attention to the uniformity of the first generation hybrids. It was discovered through an experiment in which parental forms were crossed with one contrasting trait (shape, color, etc.).
Mendel decided to conduct an experiment on two varieties of peas - with red and white flowers. As a result, the first generation hybrids received purple inflorescences. Thus, there was reason to talk about the presencedominant and recessive traits.
It is worth noting that this experience of Mendel was not the only one. He used for experiments plants with other shades of inflorescences, with different fruit shapes, different stem heights and other options. Empirically, he managed to prove that all hybrids of the first order are uniform and are characterized by a dominant trait.
Incomplete domination
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 the signs are not always in a relationship of complete dominance and suppression. So, for example, when crossing chickens of black and white color, it was possible to get gray offspring. It has also been the case with some plants where varieties with purple and white flowers produced pink hues. 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.
Feature splitting
Continuing to explore the patterns of inheritance of traits, Mendel found it necessary to interbreed two descendants of the first generation (heterozygous). As a result, offspring were obtained, some of which had a dominant trait, and the other - a recessive one. From this we can conclude that the secondary trait in the first generation of hybrids does not disappear at all, but is only suppressed and may well appear in subsequent offspring.
Independent inheritance
Many questions causepatterns of inheritance of traits. Mendel's experiments also touched upon individuals that differ from each other in several ways at once. For each separately, the previous regularities were observed. 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 traits established by Mendel were purely hypothetical. We are talking about the law of gamete purity, which means that only one allele from a pair contained in the gene of the parent individual falls into them.
In Mendel's time, there were 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 terms
Genetics is a science that studies the patterns of inheritance of traits. Mendel made a significant contribution to its development, having developed fundamental provisions on this issue. However, for them to be fulfilled, the following essential conditions must be met:
- source forms must be homozygous;
- alternative features;
- same probability of formation of different alleles in a hybrid;
- equal gamete viability;
- when a gamete is fertilizedmatched 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 natural;
- the manifestation of signs should not be dependent on the influence of external conditions.
It is worth noting that most living organisms, including humans, correspond to these signs.
Patterns of inheritance of traits in humans
Despite the fact that initially genetic principles were studied on the example of plants, they are also valid for animals and humans. It is worth noting the following types of inheritance:
- Autosomal dominant - inheritance of dominant 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 a parent is 50%.
- Autosomal recessive - inheritance of minor traits connected to autosomes. Diseases are manifested through homozygotes, and both alleles will be affected.
- Dominant X-linked type implies the transmission of dominant traits by deterministic genes. At the same time, diseases are 2 times more common in women than in men.
- Recessive X-linked type - inheritance occurs according to a weaker trait. The disease or its individual signs always appear in male offspring, and in women - only in the homozygous state.
Basicconcepts
In order to understand how the patterns of inheritance of Mendelian traits and other genetic processes work, it is worth familiarizing yourself with the basic definitions and concepts. These include the following:
- Dominant trait - the predominant characteristic that acts as a defining state of the gene and suppresses the development of recessive ones.
- Recessive trait - a characteristic that is inherited, but does not act as a determinant.
- Homozygote is a diploid individual or a cell whose chromosomes contain the same cells of the specified gene.
- Heterozygote is a diploid individual or cell that gives splitting and has different alleles within the same gene.
- An allele is one of the alternative forms of a gene that is located at a specific location on 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.
- Non-allelic genes are located on different parts of the chromosomes and are responsible for the manifestation of various traits.
Conclusion
Mendel formulated and proved in practice the basic patterns of inheritance of traits. Their description is given on the example of plants and is slightly simplified. But in practice it is true for all living organisms.
