A gene is a structural unit of inherited information. It represents a specific section of a DNA molecule (sometimes RNA). The interaction of genes ensures the transmission of elementary traits of parental organisms to offspring.
Each gene defines a specific trait that is independent of the others. They are able to interact. This is possible due to the fact that linked inheritance of genes occurs. When combined into a genotype, they appear as a system. The main relationships between them are dominance and recession.
The human genotype is thousands of traits (system) that fit in just 46 chromosomes. Each of them contains a huge number of genes (at least 30 thousand).
The degree of development of a particular trait may be due to the influence of not just one gene, but a whole series that are freely interconnected. This interaction of genes is commonly called polymerization (polysyllabicity). By this mechanism, the inheritance of skin color, hair and hundreds of other signs occurs.
Due to this number of genes, the vital activity and development of definitive organisms, consisting of various types of specialized differentiated cells, is ensured. In humans, about 200 cell types have been identified that have additional divisions into a number of more specialized functionally and morphologically cell types.
The combination of genes on the same chromosome is defined by the term gene linkage. All genes belonging to the same linkage group are inherited together during gamete formation.
In different linkage groups, the number of genes is not the same. Hybrid interaction is characterized by the fact that such coupling does not obey Mendel’s laws. However, full traction is quite rare. As a rule, all four phenotypes are represented in the offspring.
Allelic and non-allelic interaction of genes is distinguished. Alleles are forms of the same gene.
Allelic - the interaction of genes entering into one allelic pair. The manifestation of the trait is determined not only by the relationship of dominance, but also by the number of genes in the genotype.
Allelic genes are able to create relationships such as complete dominance (when there is only one gene product in the heterozygous phenotype) and incomplete (the heterozygous phenotype differs from the homozygous phenotype by the dominant and recessive traits, taking the average (intermediate) value in relation to them. the interaction of allelic genes when heterozygotes in the phenotype possess a product of both.
Non-allelic - the combined influence of two (several) non-allelic genes. It can be expressed in the form of an epistatic, complementary, polymer or modifying interaction.
The interaction of non-allelic genes can take place in different ways, therefore several types are distinguished.
Complementary - the interaction of genes that mutate independently in the same genotype and cause the manifestation of any one trait.
Polymeric is the additive effect of a number of non-allelic genes on the formation of a particular trait, which causes a continuous variation series in quantitative terms. Polymeria is cumulative and non-cumulative. In the first case, the manifestation of the trait is determined by the number of dominant alleles of polymer genes that are contained in the genotype. In the second case, the degree of development of the trait is determined only by the presence of dominant alleles and does not depend on their number.
Epistatic - suppression of one gene by a dominant allele of another, non-allelic to the first. Or suppression of the action of the dominant and recessive allele in a hypostatic gene by the recessive allele of the epistatic, which is in a homozygous state.
Complementary - a trait develops with the mutual action of 2 dominant genes that individually do not cause a trait to develop.
Modifying - a change in the action of major genes by non-allelic modifiers with respect to them. One gene may be the main one in controlling the development of a certain trait and a modifier in relation to the development of another trait.
The interaction of genes is always observed when several genes affect the formation of a certain state of any trait of an organism.