Genetics with the Basics of Selection - M.P. Myhun - 2008

CHAPTER II. Material Foundations and Molecular Mechanisms of Heredity

2.2. Modern Systemic Concept of the Gene

METABOLISM/2.html">THE CONCEPT OF the Gene as a discrete unit was introduced by W. Johannsen in 1909. Views on the gene based on classical genetics (represented by T. Morgan's school) were formed in the 1930s. It was believed that the gene is:

1. A unit of mutation, meaning the gene changes as a whole;

2. A unit of recombination, where Crossing-over occurs between genes rather than within the gene itself;

3. A unit of function, meaning all Mutations of a single gene disrupt the same genetic function.

O.S. Serebrovsky and his coworkers in the same 1930s discovered facts proving the complex Structure OF THE gene and showed that the functional unit might not be the entire gene, but its individual parts.

S. Benzer conducted the most detailed study of gene structure using the recombination criterion and the cis-trans allelism test (1961). It turned out that the unit of recombination is not the gene, as T. Morgan believed, but only a small fraction of it. Benzer proposed naming the units of recombination and mutation the recon and the muton, respectively, and the unit of function the Cistron. Thus, the units of function, mutation, and recombination can act as separate constituent PARTS OF THE gene. The main gene was called the basigene, consisting of functionally discrete regions known as transgenes.

A cistron is a unit of biochemical function of the gene—a region of the gene that carries information about The structure of a complete protein molecule.

A recon is a structural element of the gene (cistron) that is no longer divisible during crossing-over and Functions within it as a single entity (the unit of recombination). It consists of one or several NUCLEOTIDES.

A muton is the smallest region of a gene (DNA chain) whose alterations give rise to a mutant form of an Organism (the unit of mutation). A muton can be equivalent to a single nucleotide.

H.D. Berdyshev and others believe that the Definition of the gene as a fragment of nucleic acid, prevalent in molecular biology to this day, reflects only the chemical aspect of its essence. Indeed, from a chemical standpoint, the Molecular Basis of the gene is nucleic acid. However, isolated DNA or RNA is not yet a gene. The gene is a biological concept.

Characterizing the gene merely as a segment of a DNA or RNA molecule does not capture the numerous connections of the gene with The Cell or the organism. The gene is intimately linked to the cell and even to the entire organism, forming a complex biological system. The latter consists of nucleotides integrated into a system of boundaries that emerged evolutionarily, maintaining direct and feedback connections with the cell and the organism. This is why studying the systemic nature of gene Structure and function remains a central task of genetics today.

The first attempts to study the gene and its evolutionary changes within an integrated system belong to N.P. Dubinin (1929). Important contributions to a holistic systemic understanding of the gene were made by N.I. Vavilov and I.I. Schmalhausen. The latter expressed the view that systemic connections exist between genes as elements of hereditary information, and that a chromosome is a block of linked information (consisting of genes). The structure of a gene in a functional state has a qualitatively different nature than in a resting state.

A particularly significant contribution to solving these issues was made by the Kyiv geneticist H.D. Berdyshev (1972). This made it possible to realize that the genotype is not a mosaic of genes, but rather a dynamic system of connections between genes and their alleles. In turn, this allows for The Development of a systemic concept of Gene Structure and function, meaning the gene has a systematic structure. It performs its functions both as a system composed of nucleotides (lower-order systems) and as a system belonging to the gene regulatory network (as a higher-level system).

Therefore, the gene is a concept no less complex than life, death, or metabolism. Consequently, The Study of the gene never stops. It is as inexhaustible as life itself. In this regard, Ukrainian geneticist S.M. Hershenzon (1979) gave the following definition of the gene: a gene is a region of a genomic nucleic acid molecule characterized by a nucleotide sequence specific to it, representing a unit of function distinct from the functions of other genes and capable of changing through mutation.